Clemens Kruse

Hi Everyone,

thanks to the entire forum. As silent reader I was able to fix a lot of things on my c250 w204 and I'm now at 188000 miles. I have a weird issue. I have oil, that is not really mixed in in my coolant. On the attached picture you can see how it gets trapped on a kitchen paper towel. It is floating on top of the coolant reservoir. On the other side, my engine oil is flawless. No foam or anything on the oil cap, nothing suspicious on the oil dip stick.
Things I've done somehow lately:
1. A shop replaced the oil filter housing while doing the starter. The old housing was loosing oil. On the new one I was loosing coolant for some time until it stopped. I have to admit I choose an aftermarket oil filter housing which might have not been the best idea.
2. Timing chain - by me. It was the second time, because the first time I used ebay chain and vano units, which lasted about 35k miles. (I don't want to make such a cheap impression, but sometimes I have to make tough decisions.)
3. Coolant reservoir, auxiliary water pump, heater valve replaced. I had already a little bit oil in my coolant. I flushed it 4x with distilled water - fill, drive, drain, until it was clear - and then 2x with MB coolant mix. I have to confess, that when I was loosing a lot of coolant, I bought the wrong color of coolant and drove many miles with green coolant around. Mistakes were made.

My research on my oil in coolant issue shows so far:
Possibilities:
1. Head gasket
2. Crack in block
3. Oil filter housing
4. Transmission cooler

My feeling is, that my oil filter housing might be the culprit. But how can I test that it is not the head gasket or the block or anything else?

Thank you very much in advance for your help
Clemens

Odd Piggy

My feeling, doing nothing more than reading your post, is the same as yours based on what you said in No. 1.
To rule out the head gasket, a compression test should suffice. 1 or 2 cylinders that are more than about 10% lower could indicate a problem.

Clemens Kruse

That's actually the direction I needed. I ordered a compression tester. If I have lower compression on one cylinder I know it is the head gasket and I will drive it until it dies. If not, I know it is most likely the oil filter housing.

Odd Piggy

A couple of notes on compression testing since I don’t know your level of MB knowledge.
— Pull all the spark plugs.
— Use a jumper to the starter solenoid to crank the engine. If the key is used it will run the injectors and crank trying to get a start until the timer drops out.
— Head gasket leaks get worse with time.
—— They can erode the aluminum head until cannot be fixed and must be replaced.
—— They can allow pressure to get into the cooling system that can literally blow it apart.