How to Change Oil and Filter in the M110 Engine

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
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 oil filler cap
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
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
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
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.

Mann Oil filter for the M110 Engine
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.

Lower washer on the filter housing bolt
Replace lower washer on the filter housing bolt
Reinstall oil filter housing bolt
Reinstall 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 inserted into the oil filter housing
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 on the M110 engine
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 oil drip pan after oil change
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!

Cheers, Robs out!

Ultimate guide on how to change Transmission Oil and Filter in the 722.6 Automatic Transmission W140 S-Class

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, a modern special AFT blend is the alternative and has perhaps better qualities than the original blend. Make sure you get an ATF which is supported by the 722.6 5-speed, which is an ATF with MB236.14 quality. Do not use any other ATF. There are several other manufacturers other than Mercedes for this type, so look around for a good offer. The modern ATF is usually red in color and the old Benz oil was green/yellow. So it is easy to spot the difference if there is still the original oil in your transmission.

The required quantity for the S600 is 9.1L which is ridiculous! Everything is ridiculous with the flagship Mercedes. It will be less if you do not drain the torque converter, but I highly recommend you drain the entire system when doin an oil change. The smaller engines have less transmission oil capacity, so make sure you check your specific model before hoarding ATF.

You will need additionally a new filter, a new oil pan gasket, new drain plugs and copper washers, new electrical plug and gaskets and bolts. So it adds up!

Meyle Transmission filter kit
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 contains 7L of ATF MB236.14, filter, drain plugs and washers, gaskets, connector plug, a drain pan magnet, fluid cap tab, drain pan bolts. If you have the S600, remember to get another 3 extra bottles of ATF when ordering the supplies. The S400 also requires more than 7L, it needs 7,7L. All other models require less.

Meyle transmission filter kit
Filter kit from Meyle. 7L of fluid, filter, gaskets, bolts and much more!

Since Mercedes made this as “sealed for life” transmission, there is no dipstick in the engine bay. And the dipstick tube is sealed with a red locking tab. This tab breaks when you try to remove it. These can be bought as replacement or it comes with most of the transmission filter kits. So you will need to buy a dipstick in order to be certain of the fluid level after refilling. Get a cheap 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 on Ebay
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, so I would not recommend it.

Tools needed:

  • Dipstick, must be 1200 mm in length at mininum
  • Hex socket, 5mm
  • 27mm socket for M120 engine crank pulley
  • Torx socket TX30, TX25
  • Torque wrench with low scale (5-25Nm)
  • Large drain pan
  • Narrow 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.

disptick level measured
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 body gallery. Now raise the front of your vehicle, either with jack stands, or drive it up onto ramps. Shut off the car and put it in Neutral and make sure the handbrake is on. You want the gear in Neutral position, so we later can turn over the engine to locate the torque converter drain plug.

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. Draining the oil is done in two steps, first the oil drain plug from the oil pan, then draining the torque converter.

Clean drip pan
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.

Transmsission oil pan bolt
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
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.

draining the Torque converter

This is a bit more tricky to drain. It is certain that you will not find the drain plug lined up for draining. So to locate it, you will need to turn over the engine by hand. Therefore the transmission must be placed in Neutral position! The torque convert bolt should be accessible at the front end of the transmission through a small access hole.

722.6 torque convert drain plug
Access hole for the torque convert drain plug is nearest towards the oil pan. Torque converter must be rotated for us to locate the plug.

The engine can be turned over by hand by inserting a socket into the crank pulley and rotating it clockwise (looking towards the engine from the front of the car, all cars have the rotation of the engine clockwise). First you need to take of the lower front plastic panel for access, the screws are easily found.

crank pulley M120 engine
Location of the crank pulley. The engine can be rotated by inserting a socket and turning the engine clockwise.

If you have the M120 engine, grab a 27mm socket and a large socket wrench for leverage. The engine can be a bit hard to turn over due to the vacuum in the cylinders. See clockwise arrow direction of the lever movement on the picture below.

turning the engine over by the crank pulley
Turning the engine over by hand by the crank pulley bolt, with using a socket and a lever. Must be done in a clockwise direction seen from the front of the engine.

Get a helper to look for the drain plug, this is preferable. If you are doing it by yourself , you need to constantly be checking between turning the engine slightly. This might take a while if you are unlucky with the position of the drain plug. The procedure can be sweaty, but a longer lever will make it easier. Do this procedure until the torque convert bolt is showing up and lined up straight over the access hole.

torque converter drain plug
Torque converter drain plug lined up for loosening.

Now comes a tricky part. You need to loosen this plug without loosing it inside the transmission bell housing and without showering yourself in transmission fluid. There is a lot of fluid here and it will shoot out with great force. Make sure you have the drain pan lined up under the transmission. Carefully loosen the bolt and when its becoming loose, be ready to lower the bolt straight down and out of the way like a ninja. If you end up loosening the bolt into the drip pan it is better than loosing it inside the bell housing.

draining the torque converter in the 722.6 tranmsssion
Draining the torque converter. It contains a lot of oil and will drain a while.

There is a lot of oil in the converter and you will have to wait a bit until the dripping stops. When the dripping stops. Replace the old plug with a new one and a new copper washer in the transmission filter kit. This will minimize chances for leaks and is recommended. The plug must not be over torqued since the torque converter is fragile. Torque this plug to 10nm, which is quite a lot for this size bolts. Much more force and it will strip for sure.

torque converter drain plugs
Old vs new torque convert drain plug. Should always be replaced with a new washer.

Removing oil pan

Transmission drain pan bolts
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.

Cable fastener transmission
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.

Transmission pan with oil
Bottom of the transmission pan. Oil is old and very filthy. Some sludge is present. Notice the lack of a magnet from the factory.

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
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 slot
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.

Transmission valve body
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. Make a hard slap to the oil filter where the oil filter neck goes into the valve body. It will snap in place. The filter might feel a bit wobbly, this is normal, but make sure it is pushed all the way in by smacking it.

Transmission oil filter fitted
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
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.

transmission connector tab
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
New transmission connector housing. Notice the little bolt down in there
7mm socket to transmission cable housing
Use a 7mm socket to loosen the bolt for the transmission cable housing
taking out the transmission connector housing
Use 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
New vs old transmission connector housing. Notice the placement of the two gaskets.
Transmission connector pins
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.

new connector housing
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
New connector housing in place, without further leaks

Replacing oil pan gasket

Clean the transmission oil pan thoroughly and throw away the old gasket.

transmission oil pan dirty
Clean up old sludge in transmssion oil pan
New vs old transmission gaskets
Old 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.

Cleaned transmission oil pan
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 pan
New bolts for oil pan
Remember 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
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.

Drained fluid quantity check
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.

Transmission oil refill
Use a small funnel in the dipstick hole before pouring.
Pouring in new transmission fluid
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
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.

Cheers! Robs out!

How to change Engine Oil and Filter in the M120 Engine – W140 S600

The W140 How To.. articles are too and far between, especially on this site. Gladly on my part (sadly for you guys…) there has been very little wrong with this car and there’s not much maintenance either since the S600 has not been used as a daily driver. The W140 appears to me as a very over engineered car with an extremely durable design. As mentioned in the review, it is quite heavy due to all the extra sound dampening and extra equipment for comfort. I have never been in such a quiet car ever. Rolls Royce is probably the only comparable here. But as any other car, it too require regular maintenance such as oil changes. So how do you change the oil and filter for the engine in the M120 V12 engine. Sounds a bit scary right?

Preparation

This Mercedes model was one of the last one without the common OBD2 interface, and it is not required to a use any electronic diagnostics tool to reset some car computer during the oil change. What you need though is a lot of oil, 10 Liters. Remember to get an oil filter too, please get a good German known brand since they will last longer, not disintegrate and not ruin your engine. The price is anyway insignificant at this point. You don’t want to cheap out here, trust me.

Another tip is to get 2 new air filter elements since you will be messing with the air filter box anyway. And since they are cheap and should be replaced regularly it is a good time to change them now.

What type of oil then? Well it kinda depends on the conditions used, warm climate vs cold, harsh driving vs. balanced etc. I am using the car mainly in summer in a moderately tempered climate and use the car quite balanced. So no need for high performance or very cold weather conditions. However the engine is quite large and is quite slow to get up to operating temperature, so a thin cold start oil is probably beneficial to avoid unnecessary wear and tear when the engine is running cold the first 5 minutes.

I have used Castrol’s recommendation chart and it recommended the 0w-40 Edge fully synthetic oil. This is not an ad for them, but easily available here. I am also a fan of Mobil1, where I have used 0W-40 SHC Synthese Technology.

Engine oil and filter - Mobil1 0W-40 - Mann Filter
Mobil1 0W-40 and Mann Oil filter

You will also need a special oil filter cap tool which can be acquired quite cheap from any car parts supplier. The cap is tightened to 25Nm and is nearly impossible to remove by hand. It’s also made of plastic so it can break, a new cap is not cheap. The trick here is however to get the correct one since there are hundreds of different ones. I spent quite some time to figure out the correct one without actually looking in the car and measuring. Firstly I couldn’t travel physically back then due to the lock-down and secondly I didn’t want to fiddle with the car just to find out the specs for the tool. (The oil filter cap is not visible by just opening the hood and requires removal of the air intake box). The oil filter removal tool is 74mm width with 14 slots.

Parts and tools

  • Oil filter (oil filter comes with new oil filter cap o-ring and a copper washer for the oil drain plug)
  • 11L of Oil, your choice, e.g. 0w-40 fully synchetic
  • Oil filter cap removal tool. 74mm 14 slots

Procedure

The oil removal process can be done with a oil suction pump inserted from the top of the dipstick tube and then removing the drain pan plug after, this makes less of a mess and is done in most workshops. However then you need an extra tool, so this guide will only use the drain plug method.

The engine should have normal operating temperature while changing the oil, since the oil will drain out easier, so take the car out for a drive before or plan to do the oil change straight after a trip.

S600 Oil dipstick before oil change
Oil dip stick before oil change. The car has run about 15.000km since last oil change and the oil is still very clear in color with a slight hint of brown. The engine has received zero refilling of oil during this time and is still showing max capacity. I’m very impressed.

Start by lifting the car up in the front and place it on jack stands in order to access the oil drain plug. Some of the w140 have plastic panels hiding the drain plug, so make sure to remove these. However my car does not have them and the drain plug is easily accessible. Before draining the oil from below, the oil filter must come out to allow better drainage. After opening the hood it can be very confusing locating the engine oil filter housing, and in fact you cannot see it unless you remove the left side air filter box. It’s well hidden below it.

Location of engine a oil filter housing on the M120
Location of engine a oil filter housing on the M120. Hidden below the left side air filter housing

Thankfully it is easy removing the air filter housing. It’s attached by two bolts and a couple of clips to the intake housing. You also need to disconnect one airflow sensor cable. Take care not to loose the intake hose clips into the engine bay which can be hard to recover, since they can come loose by themselves after loosening the air box. Loosing such a clip will make dirty air potentially enter the engine since it can then bypass the air filter.

Removing engine oil filter cap
Removing the engine oil filter cap. Almost impossible to unscrew by hand, so the tool is highly recommended.

After the left side air filter box is removed, you can now access the oil filter housing and remove the cap with the special filter housing tool. Use a joint on the socket to make the operation easier since access is poor down there. Pack a lot of paper and keep a tray on hand to avoid spilling oil when taking out the oil filter. Clean up all of the spilled oil, since it’s hot down there and we don’t want smoking and fires while the engine is running. Also use a small suction pump or syringe to get the little left over oil which lies in the house after the old filter is removed.

Oil filter housing M120 engine on w140
Empty old oil in the filter housing with a suction pump or syringe.

Then it’s time to open the bottom oil drain plug. You will need a large oil drip pan which can have at least 11 Liters. Beware the engine oil is hot and will come out with great force when removing the drain plug. Use plastic gloves to protect the skin and try to not loose the bolt into the pan when removing it. Expect about 10-10.5 liters of oil to drain out. It’s nearly impossible to drain it completely of 11 liters by just removing the plug as with most cars.

Draining engine oil from the M120 engine
Draining engine oil from the M120 engine.

When the oil has stopped draining after 10-15 minutes. Change the copper washer on the drain plug that comes with the oil filter kit, and the reinsert the drain plug. Do not over tighten since it will ruin the threads in your drain pan. Tighten the drain plug bolt to 30 Nm. It have happened a few times over the history that people have forgotten to insert the drain plug bolt and poured in the new oil which just lands on the floor. Do not stress and make this mistake!

New vs old oil filter
New vs old oil filter

Then replace the O-ring of the oil filter cap with the one that comes with the oil filter kit. Many recommends giving the O-ring with a coat of engine oil before assembly. I have no idea if it’s any useful, but I did it. It gives at least some less friction when installing the cap. On most cars it’s good to fill the oil filter hosing with oil so the first few rotations of the engine will have faster access to the new oil, but on this car it is not possible at all. Pouring new oil into the housing will just drain straight into the block. Also it is not possible to install the oil filter without it being attached to the cap itself, so there is no chance here.

The oil filter is installed by popping the oil filter to the cap and then inserted into the filter housing. Tighten the cap to only 25 Nm and it’s very important to not over tighten here since it’s made from plastic and easily strip threads. And a new cap is very expensive!

Drip pan bottom
Bottom of the drip pan. Inspecting for sludge and metal shavings can tell you a lot about the health of the engine. Here it’s all good and in good health.

Also inspect the bottom of the oil drip pan, look for sludge and which can indicate overdue oil change interval and metal shavings which can indicate excessive wear in bearings and pistons. In my case it was no such indications and all is good.

Double check drain plug and oil filter cap is secured. Before poring in the new oil you need to know how much to add so you’re not over filling the engine. Adding 10L should be enough, but measure before you pour the last liter in.

dd fresh oil using a funnel to avoid spilling oil all over the engine. After you have filled the quantity you need, measure with the dipstick and inspect it’s not above maximum level. Some of the oil will need to get into the filter and you probably have to add slightly more after the engine have run a few minutes.

Refill engine oil
Refill engine oil into the M120 Engine. Oil capacity 10L

When starting the the engine, make sure that you get good oil pressure quite fast, and inspect for leaks in the drain pan and around the oil filter cap. After the engine has run for a few minutes, turn it off and measure the level with the dip stick again. Add oil if necessary, but do not over fill. If too much is added then you need to remove the excessive oil with a suction tube.

Reinstall the air filter box. Now It’s a good time to also change the two air filters on either side of the engine. No tools required here, it’s made like a drawer, just like how you store your underwear and socks at home.

Then take a short drive of 5-10 minutes, see that you have good oil pressure and that the engine feels normal. When coming back home, inspect for leaks around the oil drain plug. And remeasure the oil level with the dip stick, add a bit oil if needed. Then you are done for another 10.000-15.000km.

Robs out!

How to change engine oil and filter in OM617 engine

This is one of the first things you will perform when learning to DIY your car. Changing engine oil is easy and satisfaction is high when you know you performed preventative maintanence. Regular oil changes on the 617 engine will literary make it run forever and ever and ever and ever and ev….. until diesel is forbidden.

If you drive in harsh conditions and only doing short trips, you should change oil more often than 10.000km, if you are living in the flat lands and only doing long drives on highways, then every 15.000km might be enough for you. I recommend every 10.000 especially dealing with these older cars where engine wear is more prominent, also easier to remember than the other numbers.

Preparation

Buy some engine oil, you will need 6.5 liters for the non turbo 617 engine. Determine which condition you need to drive your car in, hot or cold weather. I will do a short introduction to oil “weights” which are the numbers you see indicated on the oil can. Also decide if you want to use fully or part-synthetic oil. While modern cars normally use fully synthetic oil, these older Benz are actually made for using part-synthetic oil. However this is up for preference, I won’t discuss which one is better. On my part it seems that the fully synthetic oil is easier leaking out of gaskets than the part-synthetic one, but I cannot confirm this. I have used both types for the 617 diesel.

Oil Viscosities.

The numbers tells about the viscosity of the oil at different operating temperatures. The higher the number, the higher the viscosity. Low viscosity gives less friction, but don’t give as much lubrication. Usually you will see a number like this: 5-40

The first number indicates the viscosity when the engine is cold, while the second number indicates the viscosity when the engine is warm. To ease startup the engine oils are engineered to give less friction when the engine is cold and it will start to thicken when the engine comes to operating temperature giving better lubrication.

The handbook in your car will tell the recommended viscosities at different ambient temperatures. The higher the viscosity on the the second number will make the oil more expensive, race cars have up to 50 and 60. If you choose to have 40 it is more than good enough. Living in cold Norway where temperatures can drop below -25°C easily I used 5 viscosity on the first number which made startups easier on the battery.

So to sum up the preparation you will need:

  • Engine oil
  • Engine oil filter and filter gasket
  • Oil collector
  • Paper towels
  • Basic tools

Oh and don’t wear your fanciest white pants and shirts for this job!

Procedure

Have paper nearby in case of spills, plastic gloves are smart unless you want to look like a real mechanic while going to your desk job the day after (actually for the rest of the week). If you are agile you don’t even have to jack the car up for draining the oil out, the W123s have a good ground clearance and you have room enough for a low oil collector under the pan. Have a 13mm socket ready. The engine should be warm while doing the oil change so more of the crud will come easier out.

Start by removing the oil filter cover. Wait with removing the oil filter itself unless you want oil all over your engine.

oil filter cover
Remove oil filter cover, wait with removing the oil filter itself.

Unscrew the oil pan bolt. Keep in mind that the oil will come shooting out at you and it will be warm, be careful not burning yourself. Also hold on to that bolt so it don’t fall into the oil collector. Let the oil drain for 15-30 minutes until it completely stops.

oil pan plug om617
Place the oil collector under the oil pan and remove the plug.

Remove the old oil filter, try not to spill oil all over the engine bay, protect with old rags. Watch if more oil comes out of the oil pan, I usually wait another 10 minutes.

oil filter housing om617
Empty oil filter housing.

oil filter om617
New oil filter and gasket.

Reinsert the oil pan plug now before doing anything else so you won’t forget it! I laugh every time when hearing about stories where people have filled up new oil and it just runs straight through onto the ground again because they forgot the oil pan plug. Take care not to over tighten the bolt, use only 40nm of torque, there is a copper washer there to seal, replace if it’s lost. Also clean the underside of the pan for oil. So you can more easily spot leaks later.

Insert new oil filter. Replace the oil filter lid with a new gasket that follows the new filter, put a thin film of the engine oil on the rubber gasket. Tighten the the filter lid. It is not necessary to tighten this much at all, just enough so the rubber seal sits nicely.

oil filter om617
Install new oil filter in the oil filter housing

Open the oil filler cap and pour 5 liters of new engine oil into the engine. It’s good to use a funnel unless you are a pro at pouring into small holes. Wait a couple of minutes for the oil to collect in the oil sump. Then start the engine and let it run for 1 minute. Check the oil level, pour up one liter more, check the oil level again. If not full, pour up the last half liter while checking the dipstick not to overfill. If there was some old oil left in the engine the maximum capacity of new oil i less than 6.5 liters, there is also residue oil in the oil cooler.

Clean up your mess, pour the old waste oil into the empty cans from the new oil you just poured into the car. And check under the oil pan for leaks again. If no leaks take a short trip to see if engine is running smooth. Then after the little trip check the oil pan for leaks again and check the dipstick for oil level, if not completely full, pour a little more of the new oil into the engine until full.

That saved you lots of money on workshop bills. Workshops tend to overfill a bit too which is not recommended. Your level should be under max, not over it.

Cheers!