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, A lot with a big A, 11 Liters to be exact. 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 ended up using 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.

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.

Before poring in the new oil you need to know how much to add so you’re not over filling the engine. Simply adding 11 liters will most be too much. So you should always measure the quantity of oil which was drained. In my case it was slightly above 10 Liters. 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, then start poring 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. Turn on the engine, see that you get good oil pressure, 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.

Then 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, like how you store your underwear 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 oil if needed. Then you are done for another 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!