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 adjust the valves in the M110 engine – Part 1.5

Part 1.5 of valve adjustment of Mercedes M110 Engine. Stuck valve adjusting nuts require a DOHC valve compressor tool, which is hard to obtain for this engine.

Christmas came early..

Notice the part 1.5 nonsense, what is that all about you might think to yourself? Have I gotten mad over New Year’s? It’s rather just because of the half usefulness of this article. Since you readers are mostly DIY mechanics and Mercedes enthusiasts, I want to convey a story of the journey toward valve adjustments of such an old engine. In this way we share the ups and downs, the challenges and successes, and maybe learn something on the way.

Remember in Part 1 https://mercbenz123.com/posts/valve-adjustment-m110-engine-part1/ where I ended with 4 different options listed with increasing price and pain? Well since Christmas came early (2018) I ended up somewhere with a solution in the middle of option 1 and 2. After trawling the used car tool market, mostly ebay, I managed to find a seller which sold a late 70s vintage Mercedes valve compressor kit for DOHC engines. Although not specific to the M110 engine it is close enough, that with a few modifications it might just work. Let me just say it was the most expensive vintage tool I have ever bought. Lets hope it can come to good use!

Mercedes late 70s DOHC valve spring compressor tool.
Mercedes late 70s DOHC Valve spring compressor tool for several engine models.
M110 DOHC valve compressor tool
This is the M110 engine specific tool which is out of production. Looks similar right? Although not the same, I’m sure we can adjust the obtained one to do the same job with some modifications.

I almost did not buy due to the high asking bidding price, but after the deadline was reached it was still for sale. I decided to go for it as a Christmas present for myself and bid on the tool for a little less. Chance happened that we compromised and reached a fast deal. Two weeks before Christmas it landed in the mail box.

Valve spring compressors
It came with 4 different valve compressors. I might use the second from the left with some modifications.

It comes with 4 different valve compressors, although I’m not sure if any of them fit right out of the box. I might need to adjust one of them. The lever bar has a simple screw on attachment to swap out the compressor ends. The Hook is not attached, but can be placed in different grooves. I might also need to adjust the arrangement here as well.

Under I have tried to visualize how the tool is operated on the valve head. The idea is to compress the valve just enough so I can slide off the rocker arm. Since the valve clearance adjusting nuts are so tight we need a socket over the nut which is naturally blocked by the rocker arm.

I tried to overlay this tool over the valve and camshaft arrangement in the M110 engine. Here The sizes are not 1:1 but illustrates the point. Already here we can see that there might be clearance issues between the engine wall and the compressor. Also the circular edge for the compressor surface has to be cut, so it can slide onto the valve top under the rocker arm.

I’m excited to see how the tool can be used in real life, but since it’s winter and the car is hidden away, this have to wait until spring. I’ll keep you posted on the progress in this journey as soon as possible.

Cheers! Robs out


Other news: I tried to sell the S600 in the autumn, but was unfortunately little interest which is hard to believe when regarding the current economics and huge interest in classic cars. Norway is a weird country.. The car is in mint condition with low mileage so I will not give it away for free. I will instead keep it and enjoy it, make some good articles about the w140 and let time mature it into a true classic.

How to adjust the valves in the M110 engine – PART 1

M110 Engine Valve adjustment – Part 1

I planned the valve adjustment job to be straightforward and easy, making it a delight to write an article about afterwards, but no! In the end I could not even adjust a single valve out of the 12 in total, and this is why I will divide the so called adventure into multiple parts and share my experience on the topic.

“Mother nature beats father engineer every time..”

Valve adjustments should be done every 15.000 km which means for most people every 2. or 3. year and is important for engine performance and fuel consumption. Neglected maintenance can even end up wearing your cam lobes prematurely if they get too tight!

A story of success

I got all the parts I needed, that is really only a valve cover gasket set. I let the car stay overnight for the engine to cool down. Then I start pulling out the spark plug wires, no need to mark them with cylinder number..haha! I unbolt the valve cover in a breeze, the nuts I throw somewhere neat.

Then I check the valve lobe timing, oh see that the first one is perfectly aligned already so I can start adjusting the first valve immediately. I find my valve feeler gauge easily from the toolbox and it’s not rusted together at all. I adjust the first valve and since my memory is faultless I can easily keep track of all the valves I have adjusted and the ones who are left. The crank is so easy to turn by hand and I don’t need to remove the radiator shroud or anything silly like that. I get everything done in under a less hour and bolt everything together with the new valve valve gasket and I’m now already on my way to the race track with 40 more HP.

A cake, but it's a lie

This is all however a big lie.

Sometimes wisdom words are painfully true: “Mother nature beats father engineer every time..”. The real struggle you can follow below.

bleak Reality

So before starting you should take care of a few things. In theory a valve adjustment is easy and requires little preparation and engine know how. You need a new valve cover replacement kit, since your old one is probably leaking oil and a new one is very cheap. The valve adjustment can be made either when the engine is warm (just after driving) or cold (20°C). I really recommend the latter since you will not burn your fingers and get better results since the engine is not cooling down slowly. Ideally it should be at ambient summer temperatures in the shade. You have to leave the car overnight to properly cool down after driving so this have to be planned in advance.

The tools you need is just really a spanner and some feeler gauges for the adjustment and a socket for turning the crank over, but as we will see here this is not the case for my case.

M110 engine with air filter off
Marked spark plug wires.

I start by removing the air filter housing to access the valve cover freely. Then I mark every spark plug wire with a number on a piece of tape. Usually the spark plug wires are different length, but it’s so much easier to plug them in afterwards. Then I take out the spark plugs.

Now I can start removing the valve cover bolts and place them somewhere safe. I note that the middle ones have a copper shim which I can keep, but the new valve cover gasket comes with replacement ones. It’s always nice to keep bolts, nuts and shims if they are in good order.

M110 engine with valve cover open

NOTE OF CAUTION
With the valve cover off is is extremely important to not drop anything into the engine like a nut or something, since this will cause catastrophic engine failure. Also keep dirt away and exercise hospital  level cleanliness while the engine is open. Cover it always when not working on it, like lunch break etc..

I then go in the the toolbox to find my gauge feeler blades and realize they have rusted together and end up throwing them. I go in my dad’s old toolbox and luckily find some that are in a bit better shape. With a cold engine the inlet valve clearing should be 0.10 mm and the exhaust 0.25 mm. I draw a diagram over the valves so I can mark them after every adjustment, it will be very hard to keep track of otherwise. Just try remembering 12 boolean positions for reference!

Valve gauge feeler tool

Of course none of the valve lobes are pointing  directly vertical for any of the valves after opening the cover, that would be too easy! So I go ahead and try to turn the crank, but come over a problem. The fan shroud is too tight to engine for me to get any socket tool and ratchet to the crank. Loosening just the fan shroud is not helping either since the fan is sitting tight to the shroud. Then I loosen the fan and I can just get enough room for the ratchet and finally being able to turn the crank.

I align the first cam lobe and is ready to check the valve clearing. I expect most of the valves to be to bee way too tight, and the first one is as expected. I grab my spanner to start adjusting, but the valve adjusting nut is not moving at all. In fact I’m starting to slightly round off the nut. I stop before I ruin it. Then I quickly check a few other valves, they are all tight as expected, but also here the valve adjusting nuts are super tight. I am totally stuck.

After searching the Internet for similar issues it seems this is a common scenario for these aging engines. The nut material is quite soft and can easily be rounded off when they are tight. The solution is to remove the rocker arms to access the whole nut so you can get a socket over it to exert more force.

Seems easy right? To remove the rocker arm you need to depress the valves somehow. They are under very high pressure from the valve springs and a special compressor tool is needed. There are many different DOHC valve spring compressor tools on the market, however the M110 engine have very tight space between the cams and the engine walls where the spring compressor have to fit.  And the valve is at an angle so the tool need to be just for this purpose. There is such a speciality tool for the M110 engine, but I can’t find it on a single place on the internet.  It turns out it is in fact out of production. Fuck!

I am stuck and have to abandon my job and put everything back together. This was a waste of time! (But in the back of my cynical mind I think it can be turned into an article at some point..)

Here is a diagram over the valve assembly to illustrate the point better.

Valve Configuration M110 engine

The valve compressor tool is like a leverage bar with a hook for the cam axle and a crow foot depressor at an angle that can slide between the engine wall and the cam axle down on the top of the  valve. It looks like this:

M110 DOHC valve compressor tool

how to solve the tool problem

I have considered some options below and ranked them from easier/cheaper towards more expensive options.

  • Obtain the tool

I have really tried to find this on the internet, but with no success. I think I will not be able to obtain it. Not sure if Mercedes has one , but I am scared of even asking, it’s probably super expensive.

  • Make the tool myself

I know how it looks like and roughly the sizes. I can easily obtain some steel, and a crow foot. I have a welder so I can make the tool. However I expect it to take some time to assemble. Definitely worth looking into.

  • Take the car it to a workshop

I can just take it to a workshop and tell them to adjust the valves, but they are going to run into the same problems like me and they might end up ruining the valve nuts unless I explicitly tell them the problem in great detail. Remember these days no cars require manual valve adjustment and only the more experienced mechanics have done this. If you want things done right, better do it yourself.

  • Contact Mercedes on how the fuck….

This is my last option and will consist of asking if they have such a tool, and if the tool is not for sale (or out of production), if they can at least adjust the valves if they can send a tool from Mercedes Classic in Germany to their workshop. Problem is that is going to be very expensive for a simple job. Not likely I will venture down this path. Also would turn into a dreadfully boring article for you DIY people!

More on this adventure when we return in Part 2 of the valve adjustment nightmare… soonish

(Not really, it’s damn winter and car is parked)

Cheers, Robs out!

How to change the Thermostat

Changing the Thermostat

Too hot or too cold engine will result in power loss and inefficiency in the combustion process. In the worst case total engine failure. The thermostat is actually a wear item that should be changed every 5-8 years. In some cases even between every season if you are living very far north where the winter temperatures varies extremely much between the summer season. I think this applies even for Norway especially in a Diesel where it’s difficult to get the engine warm in the winter.

Is your engine experiencing climate change?

So how do you change it? Is it difficult? I will tell you all if you hang on with the article.

Preparation

Parts you will need

  • New thermostat. Thermostats have different temperature  ranges where it is fully open, check with the manufacturer/ owners manual what is recommended for different ambient temperatures. For cold weather thermostats that open later are common, i.e. it will open at a higher engine temperature.
  • New upper radiator hose and clamps? Evaluate the condition of the upper radiator hose, change if it’s worn. Since a broken radiator hose might cause catastrophic engine failure. Also the hose clamps might break if they are old and rusted.
  • Engine coolant.

Tools

  • Screwdriver
  • coolant catcher/pan
  • Funnel
  • socket tools
  • Wire brush

Procedure

Start with emptying the radiator coolant. There is a plug on the underside which can simply be open by a screwdriver. When it is fully drained don’t forget to put the drain plug back in. Then go to the next step.

Upper Radiator hose w123 M110 engine
Loosen the Upper radiator hose.

Now you have to remove the upper radiator hose. Each end is attached with hose clamps. Hopefully the hose clamps tightener are easily reachable. They usually can be loosened with a small socket or a screwdriver. Choose the socket if you can since you might just destroy the screw notches if it’s stuck. Be aware that more coolant might come out when you loosen it so be ready to catch it.

After removing the upper radiator hose you have access to the thermostat housing. It is attached with 3 bolts. These on the M110 engine is usually ok to get out, but on some other engines like the OM617 they are terribly constructed. Now you have to take extreme care not to ruin the bolts otherwise your quick fix will turn into a long and unpleasant affair. The aluminium housing of the water pump housing will stick to the steel bolts after some time.

Thermostat housing w123 M110
Unbolt the thermostat housing. Notice the heavy deposits of aluminium oxide on the neck.

After the housing is removed, you have access to the thermostat. Just pull it out with your hands. Also note the placement of the rubber gasket. This have to be replaced by the new gasket which comes with the new thermostat.

Thermostat w123 M110

If you really want you can test the old thermostat by boiling it in a kettle with an accurate thermometer. When the spring opens is when the thermostat is heat rated. Probably your old one has deviated slightly from it’s original heat rating. If you are totally paranoid you can the test the new one as well!

Thermostat housing without thermostat w123 M110
Clean the housing of dirt and oil residue before putting the new one in.

Clean up the housing before putting the new thermostat in the water pump housing. Put the gasket on top of the thermostat as seen below.

New thermostat w123

Before putting it all together you have to clean off the oxidized aluminium from the thermostat housing. It is important to avoid coolant leaks in the future. This is easily done with a simple wire brush.

Oxidized thermostat housing w123
The aluminium oxidizes when in contact with water when air cannot reach the surface, such as here between the neck and the rubber hose.

Thermostat housing w123 M110
The oxide comes off easily with a wire brush. Now it will make a much better seal with the rubber hose.

The bolt on the thermostat housing should be tightened down until both the surface of the metal meets. Do not over tighten the bolts since you will end up stripping the soft threads in the water pump. Then you will be in big trouble. Use only a small ratchet to avoid the large torque. Get your new upper radiator and clamps ready.

New upper radiator hose w123 M110
New upper radiator hose and clamps.

After fitting the new upper radiator hose. You have to refill engine coolant. This is not as simple as just pouring in new coolant and closing the lid. You have to let coolant circulate and get out the air out from inside the engine.

Start by turning the heater on MAX inside the car. This will allow for coolant to circulate the entire system. Ideally you should have a large funnel which can be screwed down into the radiator, but this is a specialized tool which most of us don’t have. So start pouring coolant until you see it forming though the opening, but don’t make it full. Now you have to turn on the engine with the radiator cap open so air can escape from the engine. CHECK for coolant leaks!!! Did you remember to tighten the radiator drain plug? While the engine is running you will probably see the level decrease slightly while the engine burps, but bear in mind that coolant also expands as it heats so a level change might not be visible. When the engine starts to get warm and has burped some, try filling until the minimum mark and close the radiator cap.

Then go for a short spin. Observe the temperature gauge closely. Mine increased suddenly until over 100°C then did a sudden jump back down to 80°C when the radiator popped open. I might have had some air still in the engine and the thermostat might have been slow on the first opening since it was new. It never run above 80°C after that one time. To be on the safe side, stop the car if you see such sudden peaks in the temperature gauge.

When you are back. Let the engine cool down at least one hour, before tempting to open the radiator cap, since most likely coolant will pour out and scolding your hands. After one hour open the radiator cap and refill coolant until it reaches the maximum mark.

Cheers, Robs out!