After doing a swap from the 2.6 to the 3.0 on my w201, other than using more fuel (which I expected with the bigger engine), my oil consumption appears to be really high. I would say after an oil change I have topped up at least 3 times (1 full quart each time, so 3 qts total) in the last 2k miles. Before I did the swap I replaced most of the top end components: rocker arms, cam shaft, valve springs, valve stem seals, replaced all the rubber and completely sealed the front cover and even did the freeze plugs. The engine is a m103.981 from a w126, I know there were issues with the cam and the rocker arms on that particular engine so that's why I replaced all the old ones. Also, I did read that it does burn oil, but due to valve stem seals, which I've replaced and even checked and they all seem fine. Even removed the throttle body and the inside of the intake is as dry as a bone (which surprised me) I'm used to seeing a little oil film in there, but I did remove the EGR so that might've helped. The spark plugs are clean and have no carbon deposits on them and I don't see any blue/black smoke coming from the exhaust and engine has no leaks anywhere. Coolant was checked also and nothing in there. right now I'm running Liqui Moly 10w-40 with MOS2 and I recently topped up with the Lucas heavy oil stabilizer. Anyone have any idea or recall anything about these engines burning oil? Thanks

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1990 190E 3.0L

3 quarts in 2k miles is high but not horrible.

When the valve seals were replaced were they sorted as intake vs exhaust and definitely installed on the correct valves I.e., intake vs. exhaust?

The oil control rings may be gummed up, I’d try a chemical soak on the rings. Has a compression test been done?

For oil I’m not saying the oil you are using is wrong however I’d try a diesel rated 15w-40 such as DELO or Rotella non-synthetic.

Good luck!!!

Last oil I ran was Delo 15w-40 at the last oil change, but switched to the Liqui Moly. The valve stem seals were definitely put on correctly. I rechecked them recently and double checked them before I installed them since I had the entire engine out. I would like to do this compression test and see what it shows. Before that, I'd like to know about this "chemical soak" on the rings. I'm not really sure what that entails, but I'm guessing you mean to flood the cylinder the some sort of cleaning agent and then extract it out?? Maybe through the spark plug holes with vacuum and then change out the oil?

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1990 190E 3.0L

Remove the spark plugs, raise the right side of the car as much as you safely can to help level the pistons. Inject/squirt enough Marvel Mystery Oil into each cylinder to barely cover the tops of the pistons and let it soak for days if possible. Put the spark plugs back in loosely to keep the plug hole sealed. Very gently and slowly rock the engine a little BY HAND ONLY while it soaks. After a few days remove the spark plugs and rotate the engine several times by hand and then crank it over with the starter with the plugs removed. This will be messy be prepared with rags to capture MMO spraying out of the cylinders. I’d disconnect the coil in the beginning to prevent spark near an open plug hole in case it sprays oiut any gasoline causing a fire.

Install the plugs and start the engine expecting smoke that will need driving’to clear. Warm it up and drive it hard up hills if possible and let it coast downhill, this causes the rings to move back and forth in the piston grooves.

It would be interesting if you could do a before and after compression test but remember this soak is to clear up oil control rings, compression rings can be very stubborn to free if they are stuck.

Remember to NOT crank the engine with the starter with the spark plugs installed with any liquid in the cylinders. This will bend things in the engine.

Good luck!!!