Frequently Asked Questions



Vehicles with Active Body Control or ABC have several issues to be concerned with. This system is a fully active hydraulic system driven by a high pressure tandem pump that also controls power steering. These systems are prone to leaks and seeps but are overall very reliable with leaks at the pump or internally through th valve bocks being the most common. Pump leaks at the pulley snout require replacement of the pump. The vehicle level or bank in a turn is controlled dynamically in real-time using inputs from four level sensors and vehicle accelerometers. by routing high pressure fluid, delivered through front and rear valve blocks, to struts at each wheel. The system also has several nitrogen accumulators for dampening fluid pressure fluctuations. The valve blocks have valves with o-rings these can be prone to leaking if the fluid has fine particles of dirt in it or as the seals age. It is recommend to flush the system fluid periodically and change the filter as he fluid deteriorates over time.

If the ride height changes after shutdown persistently a fluid flush alone may not resolve the issue. The respective axle valve block may be the issues, internally leaking oil back to the reservoir. The ABC and power steering system uses several gallons of Pentosin CHF 11S hydraulic fluid. These systems are complex and diagnosis and testing should be conducted before commencing any repairs. The ABC struts have quick release connectors, given where they are located corrosion someimes prevents removal requiring the corresponding hard lines to be replaced. Never work on these systems when they are pressurized the lines have pressure bleeds near each strut and other lines can be depressurizing by cracking the line open carefuly. In many cases they are self-bleeding but several test modes are available for these systems that can be used for diagnostic purposes as well as insuring bleeding is complete. Rodeo is the most widely used and creates a rotational cycling of the strut height. This type of motion is very efficient at flushing the system. To flush run the return line into a 5gallon bucket and run a rodeo until it’s half full of dirty fluid or until the fluid runs green, while running a rodeo. Monitor the pressure stop and allow it to build if needed and do not run the pump dry. Prime the pump by lightly pressurizing the fluid container with compressed air, this is not a pressure vessel don’t explode the container.

We have had many inquiries about remanufactured pumps. I’m sure rebuild quality varies but given the pump is small and produces 200bar max pressure, and it takes considerable time to install one, we only use new OEM pumps. If you think you need to replace the ABC pump proceed only if it’s leaking from the pulley area, and or fails a pressure test, when the fluid level is correct and the low pressure concern is reproducible. If it’s just noisy and you think it’s the pump have it diagnosed by an independent specialist or the dealer before proceeding, there are often instances where the noise is not the pump.

Call us if you are having problems with your ABC system and want to schedule a service appointment.

Vehicles with semi-active air suspension or Airmatic have a few issues to be concerned with. Compressor failure can be caused by a worn or sticking relay, the compressor will run on and overpressure leading to failure. If replacing the compressor you should replace the relay, it is also useful to replace the air filter for the compressor and the inlet airline if it’s deteriorated. Burned harness wiring to the compressor is common when the relay sticks on and must be identified and replaced or the new compressor can be unreliable. Leaks are common at the front Airmatic struts on the W220 chassis S-class before 2003. A repair kit is available to retrofit these struts and repair the leak without strut removal. As these struts age the airbags can also leak, if the vehicle is W220 2000-2002 you may want to replace the strut rather than repair the top. If an Airmatic strut or air spring is leaking it should be replaced. A new strut is always the best solution but aftermarket remanufactured and Mercedes remanufactured air struts are available in many cases at half the cost of new units. Depending on the applications some are better than others based on warranty rates and we can advise you if new or a Mercedes remanufactured part is your best option.

W164 rear air springs are usually replaced in pairs. Once the parts are a certain age they can start to leak, the leaks can be positional so you may notice the car sinking when parked but it may be worse if you park on an incline. The level sensor arms on the W164 chassis can get stiff and if the vehicle is crooked or off level even when the compressor is running this could be a cause.

To schedule an appointment to Service your Mercedes Benz with Foreign MotorWorks please contact us today.

Mercedes-Benz black cased batteries are Valve Regulated Lead Acid (VRLA) and have no maintenance.  White cased lead acid batteries should be serviced regularly. The electrolyte should be topped off with distilled water at every service. Only use distilled water in a battery. Make sure the terminals are clean, and wipe it down. Use baking soda solution if you have acid on it otherwise plain water is fine. Although these routinely receive no maintenance even during services, they have a surprising ability not to dry out and still last 5 years ignored. We don't recommend overlooking battery maintenance, and the electrolyte level should be checked with any service and the battery tested. Midtronics battery testers are now routinely able to identify a battery that needs replacement without doing a load test, by using inductive tests to check conductivity and calculate theoretical output. Dealers only use this tool for warranty replacement, because it is quicker and more accurate.  

Mercedes Benz batteries are expensive but they are very heavy duty. Hold an aftermarket replacement in one hand and the factory in the other you can feel the weight difference.  The plates on the OE battery are thicker and have more surface area. They hold up better longer subject to shock and thermal cycling and don’t dry out easily. If you have to buy an aftermarket battery buy an exact fit as they can be unsafe if not secured in a collision. Interstate supplies Mercedes batteries so they are an excellent OEM source. We can order either for you.

Another overlooked point is the battery vent tube. The vent tube discharges any battery vapors or gas out of the vehicle. Without the vent tube gases collect in the vehicle or flow over delicate components such as the vehicle wiring harness. Don’t forget to connect the vent tube if present, as there are two outlets on each end. One is plugged, so don’t forget to take the plug from the old one. The other attaches to the vent tube. If you replace the battery you may want to use a vehicle memory keeper or you may have to normalize the windows, roof, steering angle sensor, code the radio, and set as many as two clocks on some models.

Call or email us if you are having problems with your battery or have questions.

Brake fluid should be flushed every 2 years because it is hydroscopic. Absorbed water causes corrosion but it also reduces the fluid boiling point. Once the fluid/water boils the gas is compressible which causes temporary a loss of braking. Small amounts of gas in the system can be from leaky nitrogen accumultors, whatever the source, any gas the system causes a spongy pedal. Flushing wth firm up the pedal.  

All but the very old vehicles will use Mercedes Benz Dot 4 fluid.  Dot 3 can be replaced with Dot 4 by pressure flushing the system.  We use Super Dot 4 which is backward compatible and used on new vehicles. SBC vehicles need to be flushed with a specified sequence when replacing the hydraulic unit and to properly bleed the system. This requires a laptop and a pressure flush machine with variable pressure. Without these it may not be done properly. Please contact us if you have questions or need this type of work completed.  Generally, using anything but the approved brake fluid from a sealed container could cause extensive damage to your braking system..

Call us if you need to schedule a brake or brake flush service.

Springs are a difficult part to look up in a Mercedes parts catalogue, and it takes a good parts advisor a few minutes to look at all the footnotes and make sure you have the correct ones.  If you are sure you have the factory springs installed note the paint marks colors and number of marks, and then provide that info to the Mercedes Benz parts advisor, as it will simplify the process and prevent mistakes.  Be careful because you may not have the original springs in your car. If the ride height looks off it is best to have it double checked.  Springs do fatigue with time, then become weaker and compress more for a given force to be applied.  

In New England with all the road salt it is very common to see coil springs broken on the bottom ends, this drops the car down slightly but this is not always noticed. Broken springs will be noisy over bumps, and sound different than most other worn components. Sacrificial zinc anodes were available for some chassis to prevent this type of corrosion damage. These parts are not commonly installed and may not be readily available. If your front end drags on parking lot curb stops it could be a good indication that you have broken front springs.

C class W203 chassis commonly have broken rear springs. You may hear a broken coil rattle around inside the rear control arm over bumps. ML W163 trucks have broken rear coil springs on the struts; these are replaced as an assembly.  E class W210 chassis have spring perches that break off the body due to broken spot welds and corrosion. Replacement perches can be welded on once the spring is removed.  Surprisingly, with this type of failure the spring is usually contained against the shock but it could come free eventually if ignored. Use caution with springs as coil springs can expand with lethal force if the correct spring compressor is not used to remove them or the tool fails.

Call or email us if you are having problems with your springs or have questions.  

Be sure to use the Mercedes-Benz coolant MB 325.1, as it is only slightly more expensive, but it is worth it. Dilute 50/50 with distilled water. Don’t use tap water if you can avoid it as water has dissolved ions, and hard water can cause precipitates with corrosion inhibitors such as phosphates. These are commonly used in many antifreeze products, causing deposits and decreased flow and heat transfer. Mercedes coolant is formulated without phosphates so hardness is less of a problem. Deionized water has sodium in it, while using distilled its preferable because it has negligible ion content. Antifreeze corrosion inhibitors packages are not all alike and considering the cost of a radiator or engine it is cheap insurance to use the OEM formulation. Mercedes uses silicates and is formulated to protect the metals in the system, particularly aluminum. Additionally, brazes, plastics, and gaskets are also a consideration. If you mix two types of coolants equally, even if the second is a universal coolant, you just halved each corrosion inhibitor concentration causing neither to be adequate to protect the system. Universal coolants can be mixed with any type of coolant without immediate damage to the cooling system, but don't ignore the fact that you are reducing the long term protective benefits of both coolants if they are formulated differently, inviting long term damaging effects.

For the most part, vehicles 2002 and later specify a cooling flush every 15 years or 150,000 miles. Mercedes 2001 and earlier are every 3 years. There are exceptions in the transition years. Later production vehicles with 15/150 service interval have a silica gel packet in the coolant reservoir that constantly replenishes the silicate concentration in the Mercedes Benz coolant helping to promote the long life. If you top off with another type of coolant such as OAT (organic acid) or phosphate based you are contaminating the factory coolant system.  Ignore color when trying to differentiate coolants, as these are added dyes and don't indicate anything specific about the components. Coolants compatible with MB coolant would be typically labeled G-05. Consider how unfortunate it would be to have to replace the aluminum heater core if it started leaking. Although uncommon, when it does occur it is usually the result of poor maintenance or ignoring the use of the correct coolants. The repair is costly and involves complete removal of the instrument panel to the firewall. The silicate formulation in the MB coolant offers very quick protection of the water pump from cavitations’ damage, while OAT coolants are much slower to protect. When cavitations occur at high temperatures under load the fluid boils in low pressure areas generated by the pump blades. When these bubbles collapse under pressure they cause tiny shock waves that blow the oxide coating off the metal. The metal can then erode and corrode since it is unprotected, causing the silicates to quickly form a coating that protects the metal and heals quickly if damaged by cavitations. The benefits of using the factory coolant make a long list; it is worth the small added cost.  Regardless of the vehicle brand, it is always best to use the OE specified coolant and follow the manufacturer guidelines for dilution.

Call or email us if you are having problems with your coolant system or if you have questions. 

Maintenance schedules may vary for individual makes and models of Mercedes Benz vehicles. The complete schedule for each vehicle is included in the vehicle's maintenance manual.

Maintenance manuals for year models between 2000 to 2010 are available for downloaded from the the Mercedes Benz USA website at

10,000 Miles

In order to protect the warranty on new vehicles, Mercedes Benz USA requires scheduled maintenance to be performed at 12 months or 10,000 miles, whichever comes first. Scheduled maintenance will include checking fluid levels, checking audible warning systems, checking the brake systems and tire pressure. Severe driving conditions may require checking additional items such as the spark plugs and interior air filters.

20,000 Miles

Scheduled maintenance at 20,000 miles or 24 months, whichever comes first, will typically include checking the oil and oil filter, checking all fluid levels, checking the poly-V-belt, checking the braking system to include the wear on the brake pads and proper functioning of the parking brake, checking the audible warning system, and visually inspecting numerous components for leaks or other wear. The dust filter and brake fluid will be replaced at this point.


In addition to required maintenance, most Mercedes Benz vehicles will benefit from regular preventative maintenance. The oil and oil filter should be changed at least every 3,000 miles. Vehicle owners should visually check the fluid levels of the battery, radiator, transmission, windshield cleaner and brake system every 5,000 miles. A visual inspection of the windshield wiper blades, head lights, tail lights, turn indicator lights, horn and tires every 5,000 miles will help to catch problems early before they can become serious.

Call or email us if you ave any questions about general maintenance on your Mercedes Benz.


If you are removing any head, open the block drains to drain the coolant below the surface of the head or coolant will leak into the crankcase when the head is removed. On engines with V configuration it can have one drain for each side. When removing the head follow the reverse of the tighten sequence and do it in stages to prevent warping of the head. In most cases the exhaust manifold can be removed attached to the cylinder head.

Mercedes Benz M104 engines from the 1990's are very commonly leaking oil from the back right hand corner. The failure was partly due to dissimilar metal expansion and the original head gasket design. An aluminum head expands faster than a cast iron block. This combined with the placement of the oil passage very close to the edge on the block. The head gaskets now have an updated design but still repeat failure is all too common. Careful surface preparation is crucial to having a good seal, often repeat failure is the result of corner cutting and poor preparation of the surface. The using of abrasive disks that are too aggressive and cut into the aluminum head surface. Mercedes-Benz does not recommend the use of abrasive disks they prefer gentle scraping or chemical removers, in the trade abrasive disks are used everywhere. If you are worried about bits of abrasive getting into your oil passages and later embedding in a bearing then either plug the open holes or be cautious of material falling into them. A vacuum can help remove dislodged material while scraping with the other. In practice using sharp scraping blades works well for poorly adhered material when done at shallow angles gently, don't gouge the surface.  If not done carefully you can cause damage that can require cylinder head resurfacing.  I prefer a combination of gentle scraping and scotch brite pads all done by hand. Finish the surface prep with 3M bristle disks available in three grades, white 120 grit, yellow 80 and green 50 grit.  Use the lightest grit possible on aluminum, and only very light pressure and keep moving.  You can plug any open oil feed passages but if the surface is already relatively clean this can be avoided. Be sure you do don’t forget to unplug them later or you will have bigger problems than leaving them open could ever cause.  Bristle disks are somewhat expensive unlike roloc disks, and they have an abrasive embedded in plastic fingers and produce very little fine debris. If you use an air die grinder most of the material is spun off radially and you can polish the surface and remove any material from small pockets. Use low speeds, light pressure, and shallow angles to prevent gouging. Another problem with inexpensive abrasive pads is that some of the fines that remain can pass through the oil filter and may continue to circulate in the oil increasing wear. With the abrasive embedded in plastic the particle is larger and can get lodged in an oil filter. Using disks for final surface prep can be a good idea, although the problems arise when they are used to remove bulk material.

Once the two surfaces are prepared be sure to check the surface for any deviation from flatness. Place a machinist bar evenly over its length to 0.0001" check longitudinally, transversely, and diagonally in two directions noting any deviation. It’s a good idea to check this before cleaning because it may need to go to the machine shop for resurfacing anyway. It must be clean enough for the straightedge to lie flat. If you can see light from a led flashlight under the bar check with a feeler gauge and quantify the measurement and make sure it is within specification. If not, it has to be stripped and sent to a machine shop for resurfacing. You can leave the valves in. If the surface is corroded it may also need to be resurfaced as this can inhibit good sealing, depending on where the damage is. A head should only be resurfaced when needed as it is not necessarily a good thing. When ready for assembly make sure both surfaces are totally clean. If oil is dripping out of the head wait until that has stopped before proceeding. Clean it just before assembly, as both surfaces need to be clean and oil free. It’s a very good idea to chase the head gasket bolt bores in the block to insure the bolts turn freely. Make sure you blow out the holes, as any liquid trapped in the bores will cause the bolts to hydro lock. A hydro locked bolt will stop turning and start twisting before the gasket is tightened completely because the fluid trapped in the bore is incompressible, causing the resulting assembly to fail very quickly. Most head bolts today are stretch bolts, which have a torque specification and an angle of rotation specification. This is typically done in three stages. The bolts stretch each time they are installed, so they have an overall maximum length specification above which they are discarded. If the bolts are loose or the head was overheated consider replacing the bolts as a precaution. Make sure the bolts threads are clean and lubricated with motor oil. Tighten only in the specified order and in stages or you may warp the head. If the surfaces are clean and oil free don't apply any engine sealant unless it is specified in the work instructions. If your work is done correctly it will seal on the first warm up, and as the cylinder gasket compresses over time the stretch bolts maintain tension and the seal. The first warm up is critical as the gasket really isn't sealed yet. Don't install the coolant pressure cap until it is at operating temperature and fully bleed the air with the heat on. If you pressurize it before it is fully warm one problem you can encounter is coolant forced between the gasket faces and this can inhibit proper sealing as the gasket face has temperature activated sealants on it. Run it up to operating temperature and let it cool off then install the coolant pressure cap.          

A common timesaver on M104 head gaskets involves blocking the chain tensioner with a wooden or soft wedge, so the tensioner is not removed or reset. Avoid this technique because the tensioner is a ratcheting type and even if wedged it could slip outwards slightly and the chain will end up too tight, upon reinstallation. A tight chain will be slightly noisy, and can wear and stretch causing the timing to be off. Removing the tensioner should be done when removing the heads. Make sure to reset it on installation or the chain will be way too tight. It has to be dissembled in order to be reset. If this is done correctly you will hear the chain tensioner advance on first start and oil pressure is applied as it is hydraulically driven, causing the sound of the chain to quiet as soon as this happens.  

The best bet here is to call or email us before trying to replace your head gaskets.


Very common ones to fail are the W220 and W210 (S class and E class) instrument clusters. W220’s are known to go dark and blow fuses, due to failed power transistors.  W210 clusters typically have garbled displays. With the cost of a instrument cluster exceeding $1000 in many cases, not including labor, we can provide other repair options to consider.  

Since many new or rebuilt instrument clusters provided by the dealer are blank they have to be coded, and the odometer set, to work correctly. Labor is around $150. If you consider the option of having it repaired, then the labor to install and remove is minimal and there is no coding to be considered.  The cost to repair is now considerably less, probably less than half. You may be without the use of the car during the repair, as the instrument cluster will be shipped out of state for repairs. 

The most repairs on instrument clusters involves bulb replacement that are done in house. The instrument cluster is removed, all bulbs tested, and any faulty bulbs replaced. The labor cost is around $76 plus any needed bulbs. The instrument cluster bulbs can be over $5 each, so replacing all of them is not usually cost effective. We typically replace any bulbs that are always on with the lights, and test and replace any others that may be out.  

Call or email us if you are having problems with your instrument cluster or have questions.


At FMW we use only full synthetic motor oil with specification 229.5 on newer gasoline engines produced after 1998 with FSS, these motors are M112, M113, M272, and M273.  On these engines we don’t use paper filters, as fleece oil filters are preferred with synthetic oils.  Newer diesel engines have a different oil specification (229.51). It’s critical to observe the correct oil specifications for each motor, both of type and viscosity range, because sludgeing, advanced wear, oil consumption and corrosion have been known to result from not doing so.  Older engines without FSS can in most cases be converted to full synthetic oil without problems and synthetic oils are preferred.  This will extend the service interval in most cases.  Because the oil filter on a pre-FSS engine with cast iron cylinder walls was designed with a service interval of approximately 5000 miles it would be detrimental to double the service interval without changing the filter halfway to 10,000 miles.  Given this extending services to 7500 miles or scheduling just a filter change every 5000 miles would be a safe route around this.

It is important to note that using conventional oils of the suggested viscosity range and changing at the recommended interval is always the best safest route to vehicle maintenance.  Because it is common for recommended service intervals to be exceeded, motors to be subject to severe conditions, short trips, and long periods of sitting, the greater protection of synthetic oil should be a consideration.  Because the benefits of synthetic type IV oil can only be achieved if it is not mixed with conventional type II and III oils, we recommended not extending a service interval until after the second synthetic oil and filter change. This is not based on a study, but on the realization that on most Mercedes engines all the oil cannot be made to drain during an oil change. Some of the remains are captured in recesses and cling in passages that don’t drain completely and will therefore mix with the added synthetic oil during the first change.  The amount mixed in this case is small probably less than a pint, so one change should be sufficient to scavenge it from the engine.

Fleece oil filters were designed for extended service intervals with full synthetic oils. They are more rigid, don’t loosen up with time, and have a smaller pore size with higher surface area to hold more material that would otherwise be in suspension in the engine oil.  On most models Mercedes uses a replaceable oil filter cartridge and not the common spin on type filter, as a result the cartridge must fit into the filter housing correctly.  Inexpensive poor quality paper filters often fall out of the filter housing during an oil change when they should still fit tightly enough to only be twisted off.  If an oil filter doesn’t fit tightly the oil can flow around the cartridge and not through it.  If it doesn’t have high surface area it can get clogged and the oil will bypass the filter when the pressure becomes high enough.  If it has a large pore size or tears more solids will continue to circulate in the engine and increase wear.  Mercedes-Benz engines can easily last several hundred thousand miles with very little wear; provided the maintenance is done on schedule and with approved parts and specified fluids if it is approved (non-FSS engines only).  Often many premature engine failures can be traced to poor maintenance at one point in the engine life.

The problem with hunting for the lowest price on an oil change it that in many cases, you will find a shop not using an oil meeting the correct specification or using poor quality filters and not performing the work correctly.  Many of the motors have no dipstick and overfilling or under filling are common problems, both of which can cause engine damage.  This occurs because not all motors in a series have the same oil capacity.  Dealers evacuate the fluid from the dipstick tube rather than draining it in all but a few engines. Draining it is fine if you are patient, but the encapsulation panels and screws under the car can be damaged when they are removed and reinstalled quickly.  Oil drain plug seals will leak when not replaced each time.  We evacuate the oil from the dipstick tube with a vacuum tube that can be placed on the bottom of the oil pan as does the dealer, if done correctly while hot this will remove more oil than can be drained due to the placement of the oil drain.

One overlooked maintenance items are the oil filter housing o-rings with as many as 4 depending on the engine model.  When performing a service we always replace these which avoids poor o-ring sealing, possible oil bypassing the filter, and more commonly external seeps and leaks when they are not replaced each time.  This may seem obvious, but it is common to see the effects of this step having been omitted, resulting in a seeping oil filter housing.  An o-ring will set on first installation and as it ages and becomes more brittle it will develop a flat face. If it is removed in this condition it must be replaced or it will leak or minimally seep when reinstalled. The o-rings are included in an OEM filter kit and there is no additional parts cost other than the labor to replace them which is included in the oil change.

Although prior to model year 2005, motor oils satisfying 229.3 or 229.5 specifications can be used, we use only 229.5 on all FSS engines.  It is important to make clear that not all synthetic motor oils satisfy the 229.5 oil specification. We currently use Castrol A3/B4 European Formula 0W-40 it is MB approved 229.5.  Advertizing costs and marketing efforts of producers as well as supply and demand govern oil prices. We make every effort to buy the most competitively priced oil that is available in out of area, provided MB approved to meet its specifications, in order to keep the cost of services as low as possible. FSS diesel engines we use use full synthetic Havoline Pro-DS Euro 5W-40 MB Approval 229.51 which has a slightly different additive package for a diesel.

Full synthetic oils have more stable shear strength with heating and even with more frequent oil changes non-synthetic oils cannot match that performance under load at high temperature.  Some have argued that if you add up the cost of more frequent conventional oil changes on older vehicles, that were shipped with conventional oil, then compare them to the longer synthetic oil service interval with fewer changes the synthetic oil is then competitive in price.  As we mentioned before the oil filter should in most cases not be subjected to the extended service interval because it was not designed for it, and the synthetic oil route will be more expensive. This is an inexpensive insurance considering the high cost of a motor rebuild or swap.

Oil capacities:

Specifications from WIS are converted from liters. These quantities are for an oil and filter change only.  Please consult your owner’s manual to confirm they are correct for your application. When changing the filter make sure you change all the o-rings and use a good quality filter. On the M112, M113 and M272 and M273 motors use a fleece filter.

M103 6.8qts
M104 7.4qts
M119 8.5qts
M120 10.6qts

M111 Engines
111.92/94/952/956/957/958/96/97/982/983 5.8qts
111.951/955/981 7.4qts

M112 Engines
112, 112.975 8.5qts
112.916, 112.953 7.9qts

M113 Engines
113.940/941/942/943/948/960/961/962/966/969/982/989 8.5qts
113.944/963/965/968/967/980/981/984/986/991 7.9qts
113.987/988/990/992/993/995 9.0qts

156 in W164 10.3qts
156 in W204 9.0qts
156 in W209, W211, W219 9.3qts
156 in W221 10.0qts
156 in W230 8.5qts
156 in W251 10.15qts

M137.970 9.5qts
M271 5.8qts
M272 8.5qts
M273 9.0qts note GL is about 10.0-10.5qts

275.950/953/980/982 9.5qts
275.951/954/981 8.5qts

diesel engines
601 6.3qts
602.91 7.0qts
602.91 w/ EGR 7.4qts
602.982 6.9qts
602.96 603.91 except 603.913 7.4qts
603.913/96/970 8.0qts
603.971 8.5qts

Call or email us to have your Mercedes Benz oil change or ask related questions.


Vehicles with semi-active air suspension or Airmatic have several issues to be concerned with. Compressor failure is often attributed to increased air demand due to leaks or from a faulty relay causing the compressor to run on and overpressure.

Leaks are common at the front Airmatic struts on the W220 chassis S-class. A repair kit is available to retrofit these struts and repair the leak without strut removal. Although less common, for other leaks the strut must be replaced.  A new strut is always the best solution but aftermarket remanufactured OE air struts are available in many cases at half the cost of new units.

To schedule an appointment to Service your Mercedes Benz with Foreign MotorWorks please contact us today.


Recommended service intervals:

  • M104 every 45,000 mi or 4 years
  • M111 every 45,000 mi or 4 years
  • M119, M120 every 60,000 mi or 4years
  • M156, M275 every 60,000 mi or 5years
  • M112, M113 motors every 100,000 mi or 5 years
  • M272, M273 motors every 91,000 mi or 5 years

Some years have slightly different intervals. Check your owner’s manual for the best information, or call us, and we will confirm it.

It helps to lubricate the threads with anti-seize as you don't want to gall the spark plug bores on removal or installation. You can also use light oil if you prefer but anti-seize is a better thermal conductor and is preferable in the interface. Galling occurs when the aluminum cylinder head threads seize and stick to the plated steel spark plug threads. Many spark plug manufacturers specify installing plugs dry as the anti-seize can increase the torque and cause thread damage. This is probably not the case but you should decrease the torque to compensate if desired, approx 20%. Just be careful the anti-seize doesn't get on the electrode as it is contains metal particles and is conductive and the spark will find the lowest resistance path to ground. Avoid the use of air tools until you are sure the spark plug is moving freely, and use a torque wench to finally install. The correct torque is important as it controls the rate of heat transfer, causing the plug to run hot if too loose. A hot plug can cause pre-ignition, occuting when the fuel air mixture ignites before the optimum piston position. This can cause peak cylinder pressures to occur before the piston is at TDC and if this occurs over time the engine pistons can be eroded and damaged. If the plug is too tight the threads may be damaged and hard to remove later. If the plug cannot be inserted and tightened all the way finger tight the threads may need to be chased with a thread chaser. This has to be done carefully by lubricating with penetrating oil if you are cutting carbon, and by greasing the recesses in the tap if you are removing metal, as it will catch the shavings from falling into the cylinders. Fortunately, overheating plugs and galled threads are extremely rare on a Mercedes if you follow the tips in this section.        

Replacing plugs on the M112 and M113 engines is much easier with the special tool to remove the wires without damaging them. This 17mm wrench was designed to adjust valves back before hydraulic lifters were common. This tool (110 589 01 01 00) is now more commonly used as a spark wire removal tool. It gives you the proper fork like opening and leverage to make a difficult removal job easy. Hose pliers and boot removal tools are other less preferable options but do work. If you do these a lot you may want to order one. Reproductions of this tool are available but the original design is open on both ends and twists in different directions, which helps when doing the back cylinders. The copies I have seen are not quite the same, although they may work well. You may also want to consider a spark plug installer. It's an all rubber tool that allows you to insert and finger tighten plugs. Cross threading is not something you want on a back cylinder where you have barely enough room for a hand. There are many different deigns including the all rubber one from Mac tools which works well. Be aware the most common source of ignition problems on these two engines are the spark plug wires. At the dealer the price of one spark plug wire is over $50. When you have 16 on a M113 this gets expensive quickly. Many times to accommodate a budget only a few cylinders are done at a time. Iterating repairs and diagnosis time can get even more expensive. We can sell an OEM wire set for a M113 for around $400 while our labor to install is also substantially less than the dealer. Replacement of spark plug wires isn't that common but if you need to do several cylinders consider doing a set. The labor to replace the plugs and the wires is substantially less than doing them separately, so if your dealer is using menu pricing, make sure you ask for them to adjust for the labor overlap.  

One other issue on The M112 and M113 engine is that the oil baffles at the top of the valve covers seep oil, and changing the valve cover gaskets alone won't stop the oil seep. The reason it appears in this section is that if usually occurs after 5 years on most of these vehicles the plugs also need to be replaced. If you can replace the plugs and reseal the valve covers the labor is reduced substantially. The seep can cover the coils and wires in oil and dirt, and although it can be cleaned up, it’s something that can be avoided if you inspect the valve covers for the need or resealing at the same interval the plugs are replaced. The oil baffles on the valve covers are resealed with engine sealant 003 989 98 20 10, the same RTV type sealant that is used for most Mercedes engine assemblies that have no gaskets. This is an outstanding sealant that forms a very strong bond when fully cured, has a 10min work time, and skins over quickly so it can be put into service within 30min. It takes awhile to fully cure but that is unimportant to its sealing qualities. Be aware it is critical that the surfaces to be bonded be cleaned of all old adhesive and dirt or any oil.  Any oil and the finished assembly will leak. It is a labor intensive repair but it doesn't have to cost $1000. I recently resealed two valve covers both baffles and replaced the plugs on a CLK 430 and the total repair was approximately $800. The dealer estimate was $925 just for the valve cover gaskets. You could pay as much as $925 and would be amazed that in many cases the valve covers go in the spray cabinet washer the gaskets get replaced and the baffles are never touched. Technically, the oil baffle reseal is not part of the valve cover gasket operation so it may not always be done. It is an additional operation and is the most time consuming part of the job if done correctly. If you are in need of this repair make sure you do both the baffle and the gasket reseal, and if you are near 5 years or 100k miles replace the plugs also. The labor overlap is considerable so it’s not unreasonable to ask if this was considered when preparing the estimate. At Foreign MotorWorks you can be sure all labor overlaps will be considered when preparing any estimate, so you don't double pay labor charges. For example if I need to remove the coils to remove valve covers or the plugs and I am doing both the total labor needs to be reduced to reflect the reality that the coils were only removed once. It is common practice for the labor amounts to be summed and no overlap considered.      

On plugs in older engines before 1990, it is not uncommon to find the incorrect spark plugs in vehicles with distributor type ignition systems. If you plan on upgrading sparkplugs you need to carefully inspect or replace all the secondary electronic parts or the end result may be carbon tracking, current leakage, and misfiring.  It is not practical or beneficial in many cases to do this. Use the OEM plug recommended for the motor. Some high energy plugs may last longer, but often have larger gaps and need more voltage to fire. If your coil can’t provide this voltage or the spark plug wiring insulation is poor, that voltage will find another path to ground. As a result the car won’t idle smoothly, making them a poor choice in this case. With sparkplugs only use the OEM parts or the results may be less than desirable even if the plugs are made of superior materials. Beyond issues of gap are subtle variations of heat range and resistance that make the choice of the correct spark plug best left to the design engineer. It's best to keep to the OEM recommendations, as there is little evidence to suggest that changing spark plugs from the OEM specification would have any benefits.  

Use caution when replacing plugs on Mercedes motors produced between 1991-1196 as the insulation on the engine wiring harness can be brittle. On a M104 engine this is very common but many of these have already been repaired by replacing the engine harness. Check the insulation on any of the exposed wires in the engine harness on the engine. The heat causes the insulation to crack and flake off. If the insulation is cracked don't touch anything unless you are committed to replacing at engine wiring harness because it may not start after replacing the plugs, or may misfire or backfire into the intake which can damage the throttle valve.    

A common cause for misfires is a no spark or weak spark condition. For anyone interested in diagnosing a weak spark condition consider this. In a vacuum the voltage required to jump a gap is high, but the voltage drops with increasing pressure reaches a minimum and sharply increases again. This is called a Paschen’s law. If you use an ordinary spark plug to diagnose a no-spark condition you may mistakenly think the spark is normal and present, but when in the high pressure environment of an engine cylinder the spark may be absent.  Use a high energy spark tester; these have very large gaps to compensate for the decrease in the needed voltage at atmospheric pressure.  The reason for this is that in a high vacuum ionization of a gas cannot assist spark generation. Gas presence is sparse in a vacuum, therefore this ionized conductor not being present results in higher energy sparks.  At high pressure ionization of a gas in inhibited by electrostatic forces caused by crowding of the ions in the gap. That’s why at lower pressures like atmospheric where an ionizable medium air is present but its concentration is still small that minimum spark energy occurs. With this mind it also helps to explain why some misfires only occur under load, because this is where cylinder pressures are highest and the needed spark energy is also the highest. Weak plug wires may not show up at idle but may turn on the CEL under hard acceleration. A high energy spark tester simulates the higher load condition where the misfire occurs. Most OBD II code scanners can also be helpful locating the problem cylinder if the vehicle was built after 1997. Beyond this ignition scopes provide the best window into cylinder ignition condition and compression, but they are seldom needed on OBD II vehicles because the on board testing is so comprehensive. Misfire recognition is very sensitive, and in case where a leaking valve may be suspected, a relative compression check can be performed electronically on some engines with a scan tool which can monitor starter draw current.  The relative current draw for a leaking cylinder will be low, that in many cases is much faster than a conventional compression check which can be performed after if needed.  If the problem can be uncovered quickly with the correct equipment the corresponding diagnosis cost to you will be the lowest. If you are doing the repairs yourself or at a shop without diagnostic technicians consider the cost of replacing unneeded components, as it may be better to have it professionally diagnosed by a specialist before replacing any parts. You can then choose to repair it yourself if desired.

To schedule an appointment to Service your Mercedes Benz with Foreign MotorWorks please contact us today.

The M112 and M113 engines built between 1999 and 2005 have been very reliable with respect to timing chains and in general. The M272 and M273 engine introduced in 2006 have had problems with the timing resulting from a worn balance shaft sprocket (M272) or timing chain idler gear on the M273. That gear may not have been hardened properly and is a subject of a class action lawsuit. The manufacturer will cover a decreasing percentage of the repair up to 125,000 miles. Check with the dealer of you have this issue with either or both codes 1200 and 1208 as they may cover part of the repair.

The repair involves removal of the engine, oil pans and front cover and all cam actuators, we replace the balance shaft or idler gear, the chain, any worn guides, the sheet metal pan if bent, the oil pump, the oil level sensor, and all parts supplied in the kit. This is a repair that we do regularly if you need it done please contact us. Due to the high cost this is sometimes put off, although it doesn’t lead to catastrophic failure it does shed a lot of metal bits into the engine and when the gear is worn to a nub we often find the guides are more worn. Some the guide require head removal to replace, so it may be beneficial to do the repair when the code is coming on/off rather than after it’s been on solid for awhile.

Modern timing chains can be expected to last the life of the engines if all the parts are manufactured correctly. We have seen some early M271 engines with broken chains, these are single row chains. If you have any abnormal engines noise on startup or chain noise you should have it checked. If your OBDII engine (built after 1997) has more than 150,000 miles on it and you have done all the scheduled maintenance chances are the timing chain is fine. If it isn't you might have code relative to the timing being off beyond a specified limit in the engine software. If it's an older engine from the 1970s or 1980s or has a single roller chain it may be needed. The only way to know for sure on an old engine or even a suspect newer engine is to check the base timing, if it’s off beyond the specification replace the chain and any worn guides. To check it, with the valve covers off rotate the engine at the crank bolt manually clockwise in the direction of engine rotation to TDC, either the cam timing marks line up or they will be off. If you are off 5 degrees of crank angle that’s 2.5 degrees of cam angle. It may require two revolutions of the crank to get the lines in a position where they can be checked. Don’t rotate counterclockwise if you overshoot TDC, you may brake a guide, over tighten the tensioner or jump timing. Regardless, you need to take up the chain slack to get a valid measurement so always only rotate in the direction of normal engine rotation.

Know the correct procedure as the M272 and M273 valve covers are bonded on and the timing is checked with the four cam sensor removed and the engine rotated until all 4 stamped circles on the pulse wheels are centered in the holes at a specific crank angle. On an installed engine this centering can be subjective with limited room using a mirror particular on a V8. The timing will be off on the right bank only, the off centering can be very slight in some cases. On a repaired or good motor it will be perfect. If the timing marks don’t line up you may have chain stretch or a worn sprocket. Installing an offset woodruff key in the crank sprocket is one solution for small corrections if you are building an vintage motor, but for anything more than a several degrees replace the chain. A chain may be up to $300 but consider the time involved to replace it later or if it fails. On an interference engine loss of the chain is loss of the engine in many cases, unless it occurs at low engine speeds. Even then valves will be bent on several cylinders, bent valves usually damage the guides on removal. If you replace the chain check the sprockets, and if blunted or rounded they should also be replaced. A worn sprocket will quickly wear out a new chain and it will cause the timing to be off. Consider chain and sprocket wear fitted parts, if either are worn replace them both. Realize that the labor to pull the front cover and replace all the sprockets is considerably more than feeding a new chain in, but it won’t last long if your sprockets are worn.

If you remove the timing chain then you removed the chain tensioner. If it’s the ratcheting hydraulic type or you may end up with a chain that's far too tight if you don’t reset it. You'll hear the chain noise if you missed this step and risk snapping a camshaft or braking the chain. To reset a ratcheting chain tensioner remove the Allen nut then the spring and spacer. Pull the pin out fully, it only goes one way. Then insert the pin in through the back make sure its not extended. Install the tensioner with the 27mm nut with the Allen nut not installed yet, torque in place. The chain should be properly installed and timed before installing the tensioner spring. Now insert the spring and spacer, compress the spring, with the Allen nut. Installing the Allen nut while compressing the spring is most easily done with an air ratchet, if you use air tools to start the job make sure to finish with a torque wrench. Some tensioners particularly on the newer engines after 2005 are disposable one use parts. They are released by turning the engine backwards at a specified torque while holding the right exhaust camshaft fixed. This presses the chain against the tensioner releasing it, as you rotate the engine clockwise from that point the tensioner will advance until the chain is properly tensioned. Know the type and design of the tensioner you are working with as this step is critical to having a successful repair.

To schedule an appointment to Service your Mercedes Benz with Foreign MotorWorks please contact us today


Early transmissions such as the 722.3 usually have recommended service intervals of every 60k. The fluid used should carry the correct specification i.e. MB 236.7 which is Dexron II D. You can call us if you want an estimate on a transmission service or need information on the service interval. We will look up and use the correct fluid unless you request otherwise. It is common to use Dexron III, but be aware fluids with the correct Mercedes Benz specification should only be used. In most cases Dexron, unless it is marked on the bottle with the MB specification, being met may not be approved. If possible we always drain the torque converter, because omission of this step leaves 4 liters of transmission fluid in the vehicle. With the onset of lifetime fill electronic transmissions in the late 1990s the torque converter drains were omitted. These transmission are controlled by vacuum and modulator pressure, which can be adjusted and have some weak areas where vacuum leaks are common.

The 722.6 has been a very reliable electronic transmission and is much simpler to repair than its predecessors. One problem that was ongoing with this transmission is leaks at the plug adapter for harness connector. There are various versions of this adapter and o-rings. Some have tabs, and the adapter is best replaced complete with o-rings. If the adapter o-rings should be black, red, or white o-rings then they are prone to leak. Connectors with tabs will also leak. The electronic transmissions are lifetime fill in most cases and have a lock on the dipstick. If you replace the adapter you need to adjust the fluid level with a special transmission dipstick tool. The fluid used is not Dexron III but a variant of it, so don’t use ordinary A/T fluid in an electronic transmission with lifetime fill.  The correct fluid is 001 989 21 03, MB 236.10. This fluid is backward compatible with all earlier transmissions. The dipstick is a special tool and the dipstick cap has an anti-tamper plastic lock. The fluid after MY 2006 is the same in a 722.6 as a 722.9. Don’t use the 722.6 fluid in a 2006. The newer fluid is identifiable by its lightly purple color. The newest fluid is backward compatible with all Mercedes transmissions. Some late model 722.6 transmissions have a scheduled transmission service, oil, and filter at 39k. Transmission service completed with the correct fluid could only be beneficial, even if it isn't called for.

Early 722.6 transmissions had a poor valve body conductor plate design. This part has the starter lock out switch and a transmission VSS sensor built into it that powers the shift solenoids. If it fails you may have an intermittent no-crank no-start condition and the transmission may shift irregularly because the speed sensor signals needed to calculate smooth shift adaptations are faulty. This part can be replaced with the transmission in the vehicle and the valve body removed, which is good to do if considering a transmission service on an older vehicle. If you are experiencing shifting concerns or start delay, please contact us for details as we can scan for codes that would indicate you need this repair or other transmission repairs.  

One note on torque converters and transmissions is there considerable variation in these parts and the best repair is installing a Mercedes-Benz remanufactured unit as it will be an exact match. Used parts will in most cases not match and may be problematic even if they are good, Control units can be very specific and may not work correctly.  Dealer remanufactured is the highest cost option but is the best and fastest turn around.  Alternately, we can rebuild your transmission, and have your existing torque converter rebuilt depending on the extent of the damage. Torque converters that need to be rebuilt are sent out for this repair. They are punch marked, cut in half by a dedicated machine and cleaned of any debris. The lockup clutches are replaced if needed and welded back together on a dedicated machine. We don't recommend replacing one with an aftermarket remanufactured one, as you are best to have the one from the vehicle rebuilt. There are too many variations of these to expect you will get the correct one, although it will fit, internally it will have a different design and stall characteristics. A new unit from Mercedes is the best repair but it may be over 3x the price of having yours rebuilt. In many cases the torque converter is replaced simply because it may be contaminated with material from the failed transmission and if it is reused the new transmission may be damaged. Having it opened inspected and rebuilt eliminates this concern.    

Another issue with the 722.6 involves transmission fluid wicking up the harness into the control module and causing the module to malfunction. Usually, the harness from the transmission to the ETC module is replaced and the module is replaced provided the leak is repaired. In some cases this may be more than is actually needed but it usually fixes the concern. Transmission fluid does not actually damage the module and can be flushed away with board cleaning solvent or electrical contact cleaner as a first attempt. Always repair the leak before replacing a module.

Another issue with the 722.6 was in Valeo radiators leaking coolant into the transmission fluid, which causes harsh engagement followed by a droning vibration. There is a glycol test to determine if this is the case. If strongly positive the radiator and torque converter are replaced and the transmission and lines are flushed. The dealer used to replace the transmission also but no longer does this commonly. If the contamination is slight the radiator only is replaced and the transmission and lines flushed. Consider having the transmission clutches replaced if the contamination is high, i.e. visible contamination. The clutches are very sensitive and it may not be fully repaired unless the radiator, torque converter, and transmission are replaced or rebuilt. If you have this complaint and the glycol contamination is not present you may need a new transmission control unit. The newest software can correct an adaptation issue with the torque converter than can also be the cause. This should be diagnosed by a specialist. The transmission control unit is replaced and adapted to repair this because the transmission software is not flash updatable as it is on the predecessor.      

The next transmission in the series is the 7-speed 722.9. It has no dipstick tube and can only be filled or checked from below. If your vehicle has a 7-speed you may have noticed that 722.9 transmissions have no hill holding capacity, and they roll backwards with your foot off the brake. Some have a hill holding feature where they use the brakes to hold briefly. The reason is this, when the 722.9 was designed it had to fit into the same envelope as a 722.6, as it was going into vehicles already designed and in production. If you change or modify the transmission tunnel you have to repeat all the crash testing as it is a crumple zone.  Since the 722.6 has five gears and the 722.9 has 7 gears, the extra Ravigneaux gear set that makes this possible that has to fit into the same package, requiring something non-critical had to be omitted. From the 722.6 design two sprag clutches were omitted. These are essentially freewheel elements that spin in one direction but lock up in the other.  Without them a transmission will not lock up when it rolls backward in 1st or 2nd gear.  If you have ever wondered why a 7-speed automatic doesn't hold a hill like the 5-speed automatic does that’s the reason, it's not broken.  

There are numerous issues with the 722.9 particularly the early ones. Contact us if you are having problems with one. These as the 722.6 can rebuilt and repaired readily.


If you have a Mercedes-Benz vehicle produced between 1991 and 1996 you may have a bad engine wiring harness. This mostly affects model M104 and M119 engines. Many of these have already been replaced under warranty, goodwill, or at the owners expense.  There is no recall or goodwill assistance on these at this time.  If you are considering any type of repair that may disturb the wiring harness on one of these engines of this year range, and are unsure of the condition, have the harness evaluated before you proceed or it may not run when you are done.  We can assist in diagnosing and replacing a damaged engine harness.  The reason this seems to occur is that the insulation may have a biodegradable component and the effects of heat were not fully realized when it was designed. The insulation turned out not to be stable to the heat of the engine compartment and then cracked and flaked off. If not replaced module damage could result.  In some cases the damage can also be present in the throttle actuator cable harness that is part of the electronic accelerator or EA. This is an expensive part where problems are rare. EAs can in many cases be rebuilt, please contact us if you need this service we can send it out for repair.

To schedule an appointment to Service your Mercedes Benz with Foreign MotorWorks please contact us today.