Changing engine oil is usually an straight forward procedure on most cars, however the location of the oil filter housing for the inline six cylinder M110 engine, makes the job a bit more messy and annoying than necessary. Now these cars with M110 engines are starting to get pretty old, which means more often oil changes with the increased mileage. My 280CE is of now 38 years old and I do regular oil changes at every 5000 km. This might seem often, but the little amount of actual kilometres this car is seeing it is usually only once per year.
If the car is parked for long periods, moisture will build up inside the block and the oil will eventually turn milky white, which can be noticed if opening the oil filler cap. If you are doing the oil change yourself, you will get a clear indication of the health of the engine. This you won’t get at a workshop unless it is a special workshop for classic cars. Who can afford that anyway?
This is an article long overdue, but since I did a lot of work on the W123 laterly the opportunity presented itself. Also got inspired by writing this since I already had an article on changing oil in the big brother M120 engine: https://mercbenz123.com/posts/engine-oil-change-m120-engine-w140-s-class/
More articles on W123 coming up soon too!
Preparation
You will need a few supplies and tools before starting on the job. Also it is best to change the oil when the engine is warm since this will let the oil drain easier. So make sure you take a short spin just before changing the oil. Changing the oil can be done in any season, so no need to wait until summer for this one. Just do it!
Supplies
6.5L Synthetic Motor oil with viscosity for your climate and use: A good all-rounder could be 10w-40.
Good quality oil filter. I recommend getting a filter from Mann, since it will come with all new washers and gaskets. https://www.mann-filter.com/en.html
Paper towels or rags to clean up oil
Brake cleaner
Tools
Torque wrench
Sockets
Oil drip pan
Ramps or jack stands
Procedure
Make sure the engine is warm and drive the car upon ramps or raise the front of the car upon jack stands. The car is usually high enough just by itself to drain the oil without raising it up, but in order to reach under to the oil filter, you need the space to crawl under it.
280CE upon ramps for the oil change
Draining the old oil
Normally you would open the oil filter can before draining the oil, but since this will literally spilling oil everywhere, you must drain the oil pan first. Open the oil filler cap to let the oil drain out easier. So grab your cleaned oil drip pan, or dirty if you do not care for inspecting the oil afterwards. It is your call. Grab your trusty 13mm socket and crank open the oil drip plug.
Open the oil filler cap before draining oil. Notice the white oil inside the valve cover due to moisture buildup. It is not because of coolant mixing with the oil. This ca has been parked for over a year due to reasons.Draining oil from the M110 engine
When the oil have stopped dripping, you can move over to removing the oil filter housing. If you have never seen it, it is a large aluminium canister located underneath the left side on the engine towards the back. See image below:
Oil filter housing location on the M110 engine. Mine says MANN on it, but it might not be the case for you. It is held in place with a single bolt.
The oil filter is held in place with a single bolt, but be prepared for oil splashing when you start removing it, try balancing the filter into the upright position since it will be completely full with oil. So be prepared to get oil everywhere and keep you mouth closed. After the oil housing is removed, clean the mating surface and the area around.
Oil filter removed from M110 engine. Clean surfaces and area around.
Replacing oil filter and washers
Pour out the old oil in the filter housing and notice the orientation of the old filter and washers. Take out the oil filter and throw it away. Now clean out the old gunky oil from the oil filter housing. Use some break cleaner and get all that gunk out and dry clean.
Old and new filter. Mann filters are high quality and comes with gasket and new washers.
Hopefully your new filter has some new washers in the pack. Replace the lower washer on the oil filter bolt which goes on the outside of the filter housing (this not a copper washer). There is a spring and a spring retainer inside the housing below the filter, keep this in the same orientation before inserting the new filter. Place the new filter with the narrow hole down and the larger hole upwards. The side for up usually has a little handle on it. Do not forget to replace the new rubber gasket around the edge of the filter housing.
If you notice in the oil filter kit that there is an additional large copper washer there with an unusual shape. This washer is for the large bolt which holds the oil pressure relief valve right next to the oil filter housing. However this only needs replacing if you see oil seepage from the area. No need to replace this every oil Change. The torque for this bolt is 41 Nm.
Replace lower washer on the filter housing boltReinstall oil filter housing bolt and place in spring and retainer before inserting the new filter.
Before reinstalling the oil filter, make sure you top up the oil filter completely with new oil. This will reduce the wear at the first startup after the oil change since more oil will be available for circulation right away. This is not possible in all engines, but here there is an opportunity in the M110 engine.
New filter placed into the oil filter housing. As a last step top up the filter with new oil until the brim.
Reinstall the oil filter carefully not trying to spill out the oil from the new filter. Hand tighten so you can feel you do not ruin the threads. To tighten you will need to use a torque wrench and torque it to 35 Nm. This is pretty tight and will prevent leakage through the housing.. Too tight however and you will ruin the filter housing. Use a rag to clean up the filter housing and area completely so you can inspect for oil leaks later.
Reinstalled oil filter and torqued to 35 Nm. Cleaned for residue oil.
Adding new oil
Before pouting in the new oil, you can inspect the old oil and see if there is any residue and metal parts at the bottom of the drip pan. My oil looked alright, not any metal particles or excessive old oil, but because the car have been sitting for so long with only short starts now and then, the oil pan had built up some gunk which came out when draining the oil. Nothing serious, but it was a good time to replace the oil for sure.
Inspecting the oil drip pan after the oil change. No metal shavings or . Only some gunked up oil residue since the car has been parked for so long.
Then at last replace the copper washer on the oil drain plug bolt and torque it to 41 Nm. Very important to put this plug back before you pour in the new oil. The engine takes 6.5 L of oil, but do not pour in all at once, pour in around 5.5-6 L and start measuring, otherwise you will overfill and have to suck up the extra oil. There is always some old oil taking up some capacity. Remember to use a funnel to avoid unnecessary spills.
When the oil level is up to the minimum mark on the dipstick, pour another 100 ml between each measurement until you are between the minimum and the maximum mark. The correct oil level measurement is only made when the engine is turned off!
Now you can start up the car an let it idle for a few minutes, and while the engine is running, go under the car and check for oil leaks. Inspect the oil filter if it is leaking and the oil drip plug. If everything looks fine, you can lower the car and take it for a short spin.
Go on a short drive just to get the engine up to operating temperature and head back home. Now shut off the engine and re-measure the oil level. If it is between the minimum and the maximum mark, the oil level is good. If the oil level is still under minimum, then add some oil to get it back to the right level. However if the level is above the maximum, you should suck out some of the excessive oil. This might be unnecessary if the level is just slightly above maximum (a few mm), since there is a natural oil usage from the M110 engine and the level will be fine soon anyway.
So DIY you next oil change and become confident in fixing your own cars!
When these transmissions came out, Mercedes marketed them as sealed for life. Turns out they need transmission oil change after all. Of course this is the case when it is vented with the atmosphere and components have wear over time. If you have passed 100.000 km which is very likely for cars of this age, then go ahead of changing the transmission fluid ASAP. Also if your transmission starts feeling more jerky than usual, then change your transmission fluid ASAP.
If you notice late shifting or if it hangs excessively on gears during revs, or even slipping, then it is possible something else that is the issue. There are so many stories around on the internet that changing gear fluid will ruin your car. This is utter bullshit since changing transmission fluid must be done as preventative maintenance. There are some cases where changing fluid will not help save your transmission, because excessive wear and damage have already occurred. Do you see the difference?
Weird shifting and limp mode can often be the result of a failing conductor plate in the 722.6 transmission. This a known failure item and can be changed by yourself. The conductor plate is the electrical connection inside the transmission, which connects the signals from the computer with solenoids that steers the valve body shifting mechanism. Replacing the conductor plate is not covered in this article..
Note on slipping gears
Worst scenario of all is when the transmission is slipping on the gears, which is most likely due to worn clutches. If that is the case the transmission would need a rebuild with new clutch plates. Changing transmission fluid will not fix this issue, and the slipping most likely will get worse afterwards, since the new oil will not contain transmission debris and the clutches will slip easier. Keep in mind the oil change did not ruin the transmission, the transmission was worn out in the first place and total transmission failure is just around the corner.
Preparation
When changing fluid, you will need more stuff than just the oil. Mercedes used a special automatic transmission oil in blend in the 90s, which was supposed to be sealed for life. Turned out that this was not the case and you cannot get this even now, AFT is the alternative and is perhaps better. Make sure you get ATF which is supported by the 722.6 transmission. ATF is red in color and the old Benz oil was green/yellow. You will need additionally a new filter, a new oil pan gasket, new drain plugs and copper washers, new electrical plug and gaskets. So it adds up!
Meyle Transmission filter kit. Comes in a neat box!
Therefore I recommend to get a transmission fluid kit which contains all these things. Meyle has one great such kit, which is not too expensive either. I highly recommend it! https://www.meyle.com/en/passenger-cars/drive-components/oil-change-kits/ It cointains 7L of ATF, filter, drain plugs and washers, gaskets, connector plug, a drain pan magnet, fluid cap tab, drain pan bolts.
Filter kit from Meyle. 7L of fluid, filter, gaskets, bolts and much more!
Also since Mercedes Made this as “sealed for life”, there is no dipstick. And the dipstick tube is sealed with a red tab. This tab you need to break off in order to remove the dipstick tube cap. These can be bought as replacement or it comes in the transmission fluid kit. You will need also a dipstick to be certain of the fluid level after refilling. Get an disptick on Ebay, there are loads of options, but make sure it is long enough. It has to be at least 1200mm long for the 722.6 if you have the M120 engine. Aftermarket versions are totally fine here, do not throw your money away on a Mercedes one when you can get literally the same function for a fraction of the price.
Aftermarket dipstick from Ebay. 1200mm long.
You can try to skip the whole dipstick tube and just fill in the amount you drained, but it should only be done if you are 100% certain that the level is correct. Usually these transmissions tend to have leaked a bit over time through old gaskets after 20+ years.
Tools needed:
Dipstick 1200mm at aleast
Hex socket
Torx socket
Torque wrench with low scale (5-25Nm)
Drain pan
Small funnel
Rags/lint free paper
Brake cleaner
Procedure
Changing the transmission oil for the 722.6 is a multi-step procedure and is a bit more advanced than changing the motor oil. The procedure is divided into a few sections below.
Warming up the transmission
Start with warming up the transmission to operating temperature, this is done by driving it before you start the job. So make sure you prepare everything before so you can jump straight into the job. 5-10 minutes driving at high speeds will be enough. Then with the car running and on a flat surface and standing still, go through all the gear levels with the gear shifter 3-5 times leaving the stick in each level a few seconds. Then put it in park still with the engine running, open the hood and pry off the red plastic tab on the dipstick to open it.
Dipstcik level measure, level here was a bit low. And notice the green and filthy oil on the paper
Now measure the fluid level with the dipstick. The way to read the dipstick is dependant on the dipstick itself, however there are two levels, one for cold and one for warm transmissions. Use the upper warm level and see how much oil is left in the transmission. Mine was quite low, certainly above the cold level but lower than the minimum warm level. Measuring before can make an indication on how much oil you need to add and if it has leaked any oil.
The main reason for warming up the transmission before the oil change is for the oil to drain much easier, since it has to pass through the labyrinth in the valve gallery. Now raise the front of your, either with jack stands, or drive it up onto ramps. Shut off the car and put it in Neutral.
Draining the old fluid
Have a clean drip pan available. Keep it clean so you can spot debris or transmission material in the old oil after you have drained. This will tell you about the condition of your transmission. Have the drip pan completely empty so you can later measure the drained quantity. This will make it much easier know how much oil you must add later.
Clean drip pan ready for draining oil
Place the drain pan under the transmission oil pan. Use a hex socket to open the drain plug. Here you might have issues actually loosening the drain plug, if it has never been opened before. This bolt can seize incredibly hard. Mine got rounded off completely and I needed a bolt extractor tool to get it out. Thankfully a new plug comes with the transmission oil change kit.
Transmission oil pan bolt
Be ready for the oil to drain out with immense speed. Be careful not to burn your hands on the warm oil. Already now you can see if the oil has been changed before and within reasonable time. My oil was very black and brown and for sure never changed since the car was new. The evidence for that will come later below.
Draining transmission oil. Notice the black-brown colour. Yuck!
The oil will drain for quite a long time so take a 20 minutes coffee break. When you come back the oil should only slightly drip out. Reinsert the plug so the dripping will stop for now.
Note on draining the Torque converter
Now is supposed to be the time to drain the torque converter, but since I forgot to do it, that part is left out here. I will update this article in the future with draining the torque converter, perhaps in coming spring/summer, since I need to do another transmission oil to completely remove out the old oil.Anyway the torque convert bolt should be accessible at the front end of the transmission through a small hole. To access it you need to turn the engine over by hand. Therefore it was important to put the gear in Neutral. The engine can be turned over by hand by inserting a socket into the crank pulley and rotating it clockwise. Do this until the torque convert bolt is shown.Alternatively you can turn just the torque converter by using a large screw driver or pry-bar which you carefully push on the torque converter itself. This must be done also in a clockwise direction as seen from the front of the engine. The bolt is loosened with a 5mm hex. Torque here is 10 Nm.
Removing oil pan
Transmission drain pan Torx bolts
Now it is time to remove the transmission oil pan. This can be a bit messy, so do not wear your nicest clothes. It is held in place with six Torx bolts. You also have to remove the bolt securing the wire on the right front corner. Undo all of the bolts then leave a couple in the corners. Now use one hand to support the pan while you undo the last two bolts and gently lower the pan to the floor. The pan will contain a lot of transmission fluid trust me.
Remove the cable fastener bolt in order to remove transmission pan bracket.
With the transmission pan on the ground, you can now inspect it for particles, shavings etc in the remaining oil. This really shows the health of the transmission. My pan looked alright, but there was noticeable sludge at the bottom. There were no magnet either. Probably the factory oil. The next clue in the next section.
Bottom of the transmission pan. Oil is old and very filthy. Some sludge is present. Notice the lack of a magnet.
Replacing oil filter
Now it is time to replace the oil filter. Just pull the old one off straight down and notice the orientation, there is a plastic tab which goes into a slot. The old oil filter might have a date on it. My old filter was from 1995, meaning it never have been changed since the car was sold new in 1996. So this explains the gunky oil and harsher shifting of the transmission after 100.000 km and 25 years. Unbelievable that it never was changed earlier, probably due to the low mileage.
Old transmission filter from September 1995. Archaeology at its best. This goes straight into the storage at the museum.
The little plastic tab on the filter goes in the slot shown below.
Location of oil filter tab slot.
It is advised not to touch the valve body too much to get dirt on it, but you can inspect it and wipe it off slightly with a lint free cloth. However the transmission will continue to leak so maybe just leave it alone. If you need to change the conductor plate, then the whole valve body needs to be removed. Utter cleanliness needs to be followed.
The transmission valve body. This has to be take noff if the conductor plate needs to be removed.
Now take the new oil filter and place it under the valve body, make sure the tab aligns in the slot and simply push the oil filter into the hole. The filter will not sit super tight and might feel a bit wobbly, this is normal, but make sure it is pushed all the way in.
New transmission oil filter fitted to the valve body.
Replacing transmission connector housing and gaskets
Next step is to replace the connector sealant inlet, which is located just above the valve body on the right corner of the transmission. The oil change kit comes with a new connector inlet body and new gaskets. The old ones tend to get leaky due to old gaskets and the plastic brittle due to years of experiencing heat.
Transmission connector location
The way you loosen the connector, is to flip the tab on the outer plastic ring downwards. This will free the connector which will make access to the connector plug. Just pull out on the cable and the cable should come loose.
Flip down transmission connector tab as shown
Study the new connector housing and you see there is a little bolt in the middle of it. The old connector plug housing has to come out by loosening this bolt. Use a long 7mm socket and a flexible extension in order to get it out. It should not sit very tight.
New transmission connector housing. Notice the little bolt down in thereUse a 7mm socket to loosen the bolt for the transmission cable housingUse a flexible extension to get the connector housing out. The angle of attack is a bit tricky without.
With the bolt loosened you can just pull out the connector housing. It might be a bit stuck if the old gaskets are gripping, but just pull and it should come out. Inspect the connector pins and clean up any dirt and oil in the connector hole before replacing the new housing.
New vs old transmission connector housing. Notice the placement of the two gaskets.Transmission connector pins
Study the orientation of the connector pins so you will be able to get the connector housing in the right orientation. Pop the new connector housing in and make absolutely sure you are lined up before pushing it in. Bending connector pins will be a lengthy procedure where you will need to replace the conduction plate. Tighten the bolt just enough to be snug, do not overtighten here otherwise you will break the plastic.
Place new connector housing and tighten bolt
Now just plug plug in the transmission wire and tighten the cable with pushing the connector tab upwards.
New connector housing in place, without further leaks
Replacing oil pan gasket
Clean the transmission oil pan thoroughly and throw away the old gasket.
Clean up old sludge in transmssion oil panOld vs new transmission gaskets
Place the new gasket over the cleaned transmission and remember to put in the new magnet if your transmission oil pan did not have one already. If the old one is cracked or have shavings in it, just replace it. Also remember to replace the old drain plug and copper washer.
Transmission oil pan cleaned. Leave no trace of dirt whatsoever in it. Notice the placement of the magnet. The magnet will preserve the transmission longer and will allow you to spot metal shavings during the next oil change.
The transmission oil change kit comes with new transmission oil pan bolts. Preferably use these. There are 6 torx bolts to secure the pan. Along with aluminium spacers which you should now clean. Also clean the entire surface where the gasket will sit on the transmission to ensure a proper seal.
New bolts for oil panRemember to secure the cable in the front right corner
Hand tighten all bolts before torquing them down. Use a small low scale torque wrench which you know is good. The drain plug is torqued to 14 Nm and the pan bolts are only torqued to 8 Nm. Go around them a few times, since tightening adjacent bolt will loosen the one next to it.
Torque oil pan bolts to 8 Nm. Drain plug is torqued to 14 Nm.
Adding new transmission fluid
First see how much fluid you have drained, pour the old oil into one used oil container or similar so you can measure the level. This is especially important when you have not drained the torque converter, since you will not get all the oil out. To be precise, you will never get all of the oil out. And fluid level is more important than with engine oil. Keep in mind that you might add more id the fluid was a bit low before you drained the transmission. As was the case with mine.
Checking the quantity of the drained fluid
When you know how much quantity you can add. Start by pouring the required quantity into the dip stick hole, use a small funnel to avoid spills, also pour slowly since it will use some time to get down the long dipstick tube. Avoid spilling since it it will not be good for your manifolds to get oil on them.
Use a small funnel in the dipstick hole before pouring. Pouring in new transmission fluid slowly to avoid spills.
In order to check the level the engine must be running. Remember to put the dipstick lid back on, but do not place the locking tab just yet. Let the fluid run down into the tube for a few minutes before doing anything else.
Warm up, test drive, fluid level check and inspecting for leaks
Before going for a drive. Lower the car back to level. Then start the engine and start cycling the transmission through the gears with the leaver slowly. Do this 3-5 times with the lever in the different gears a few seconds. Then with the car still running, place it in park. The transmission is now still cold, but initial measurement must be done before driving off.
Cycling gears for transmission oil check
To measure the cold level, you will need to insert and reinsert and clean off the dipstick a few times before you can get an accurate reading. Note that the level should be not higher than the cold mark. Also note that measurement while the transmission is cold is more inaccurate than when warm. If the level is way over the cold mark, you must suck up some fluid since it is overfilled. IF OK, then check under the car that no transmission is leaking out. Take with some extra transmission fluid, the funnel and rags. Then go for a spin.
When you have been driving with highway speeds (>80km/h) for about 10 minutes, find a gas station or similar with a level surface. Do not turn off the engine and cycle through the gears again with the lever. Set the gear in Park. Then measure with the dipstick, wipe it clean reinsert and measure until you get a clear reading. If the oil level is now below warm marking, pour in only 100 ml at a time before measuring again. Cycling through the gears is necessary between each re-measurement and always keep the engine on . Repeat the process until the level is in between minimum and maximum at the warm level on the dipstick.
Finally you can install the little red tab so it can secure the dipstick tube cap.
Ever experienced that the remote IR key fob for the W140 have stopped working even after the batteries are replaced? This can generally one of two issues:
The key fob needs to be synchronised again with the car. This happens due to loss of voltage on the chip when batteries are completely dead for a while.
One component fall off due to old solder and mechanical stress over time.
Checking functionality and proper voltage
This is a very simple task. Point the IR towards your face and hold the button for one second at least. A red light will blink if the key fob works and the battery is OK. If not change batteries and look for the red blink. The battery type is 2x of CR2025 or CR2032 with 3V. If there is no blink, you need to open the key fob and maybe do some soldering. If the blink is OK, try to see if it can open the doors. If not, then it needs to be synchronised.
Here you actually see the IR diode becuase the camera picks it up. However with your eyes you will only see the red light blinking once at the lower edge of the IR diode.
Synchronising the key fob
This is a very easy job, make sure you have good batteries and the key will give a blink if you hold the button for at least one second. In order to synchronise it, go inside the car. Point the key towards the mirror and press twice at the button in rapid succession. Then within 30 seconds put the key in the ignition and turn it to position 2 without starting the engine. Now the key should be synchronised with the car. Check if it will close and open the doors. Retry the procedure if it is not successful.
Fixing loose components inside key fob
This is a bit more tedious and require you to do some electronics fixing.
Preparation
In order to do this job you will need a solder iron and some solder wire to fix it. Make sure you have flux cleaner after soldering to clean up the mess. To get the case open you need some small flat head screw drivers and a sharp and narrow knife to cut the glued case. For securing the case at assembly, you will need some glue. I can recommend Loctite 406 rapid super glue.
Loctite 406 rapid super glue
Procedure
Now you have figured out that the key fob is not blinking a red light after you swapped batteries. So you need to open the key to inspect the electronics. The plastic key case is glued together and it needs a bit of fiddling to get it open. Follow the pictures below.
Top side of key fobBottom side of key fob, here is the battery lid located.Flip open the keyTake off the battery cover.Remove the batteries.Use a flat screwdriver to slightly pry open this side. stop when you feel a resistance. The other side is glued as well and do not try to pry the whole case open. It will break.Use a knife to cut the opening this side since it is glued quite well.Cut is made and is now free from glue. It can now be pried open. Good luck!Pry open the two sides of the fob. Notice the push button component is totally loose from the PCB. This is our issue and why the key is not working. And probably the issue 95% of the cases.Make some new solder pads on the PCB for the button on the PCB. Make sure not to get too much heat on the PCB and and clean the flux off with flux cleaner.Solder the button back in place. Make sure the button body is firmly pressed to the PCB backing otherwise the button might crack loose when it is pushed next time. Make sure not to use too much heat for a long time that can damage PCB and other components. 380-400 Degrees °C is good enough.Assemble the PCB again in the lower housing. Make sure all other components have good solder. Place spring in groove of the lower plastic case. Notice the angle of the spring.Place plastic tab in key groovesPut the key in the upper plastic case and align it with spring, then turn it around a full turn to tighten the spring so the key will flip out. This might take a few tries.Key fob assembled. It will come loose without gluing, so you need to glue the case now.Put a little dab of glue here behind the keyFinish with some glue here one the other side as well.
Now your key fob should be working again and not come apart.
The video of actually starting the car is shown here. Getting it to start was a bit of a hassle, but when it started it ran totally fine. Notice the normal idling of the M110 engine after start, no fuzz even though the ignition system here is totally worn out! The last time this car was driven the engine barely could run on idle due to worn distributor and ignition wires. Mind this is many years ago, and the car is scrapped due to heavy rust. The engines still lives, 333.000km.
