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I have had Oil in my coolant for a little while now and decided after lots of research that the oil cooler was the most likely culprit. Oil in coolant reservoir, No Coolant in the Engine oil or sludge in the filler cap.
Spent a very long 12 hours removing the old cooler and replacing it with a new genuine mercedes one, From mercedes
Flushed the cooling system maybe 3-4 times each time the coolant getting clearer. now 2 weeks later the low coolant light has come on and there is fresh oil in the coolant resevoir (FFS).
Any suggestions what to try next to
1) identify the fault
2) repair it
I am a mechanic by trade however have been off the tools for 15+ years now and only worked on military equipment prior to that.
Car is a 2012 Mercedes C250 CDI Coupe with 120,000 KM on the clock.
I would do a cooling system pressure test and see if it will hold pressure without fading down. Then a cylinder leak down test might show you the problem.
I am not familiar with that engine. I have the M272 engine and have replaced my oil filter housing and oil cooler gaskets due to oil seeping from that area. Everything went well.
I found a TSB on the oil filter housing and not sure it applies to yours. I'll post it below.
My 1st thought is oil floats on coolant so maybe there is still some oil in the system and its slowly working its way out and ending up in the coolant reservoir. If so just syphon out the oil and keep an eye on it.
Coolant system pressure test noted above would be a good step.
I have questions. Are you losing coolant since you say the coolant light came on? I like to go under the car and remove the undertrays every so often to see if anything is leaking down.
How did the old filter housing and gaskets look, were there signs of it indeed leaking?
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Still Oil in coolant after oil cooler replacement
