Hey guys,

I've recently acquired a 2013 C220 CDI (manufactured in 2012) with OM651 engine. Car has very low miles (21K miles). I had the oil changed as soon as I bought the car couple of months ago. Used Amsoil 5W-40 for oil change. Yesterday, I took the car in for suspension related inspection. And the tech checked the coolant tank and the oil residue is in coolant tank. Checked the oil cap, no abnormalities. I think the oil cooler gasket is the culprit. I am ordering new oil cooler (with the oil filter assembly). I am thinking that I caught the problem in the early stages of the oil mixing with coolant in the cooler.

I've never owned a diesel engine car before. So, I have zero knowledge with diesel cars or with OM651 engines. I am hoping some of you may have seen this before and hoping you could give suggestions...

If it was me, I would take an oil sample and send it off to Blackstone Labs to confirm that there really is coolant mixing in with the oil before jumping to conclusions.

Is it originally US car? Did not know OM651 were imported here before 2014.
Anyway, oil in coolant most of the time comes from ATF and the explanation "traces" is not telling much.
Diesel motor oil turns black very fast, so it should be easy to tell difference between the 2.
OM651 is very nice engine and my E250 gets up to 60 mpg.

Car is not in US. I am currently on a long term assignment outside US. I bought this car to use it while I am here.

Since I am not in US right now, it is not easy to send oil sample to blackstone for oil analysis. If I was back in US, that is what I'd do as a first step.
I don't see any anomalies on the oil cap. Coolant is not mixing in oil. However, oil is definitely in the coolant tank. As a first step, I am replacing the oil cooler (plus the oil filter housing as a single unit) and flushing the coolant. I will continue to monitor coolant as well as oil.

Nice of you to mention it is not US car
But anyway, I don't know how much different is your OM651 from mine OM651. but the oil cooler for mine retails at $444, what is nice number.
Than in lot of European countries - mechanics charge much less than in US and paying them the time to replace seals only makes lot of sense.
But at the end I still would question your judgement.
Oil coolers on those engines are NOT reported as trouble and I read Polish forum, where members have those engines reaching 10 year of age.

Sorry, my bad.

My reasoning for thinking of going ahead and replacing the oil cooler itself is that on this OM651, to remove oil cooler (even to replace the gaskets), you have to remove power steering pump and other stuff. Then 2 to 3 times flushing the cooling system. After going thru all this work, I just want to eliminate the entire possibility of oil cooler being the culprit.

On gasoline engines (on Mercedes M272 and on BMW N52B30 engines) I have replaced just the gaskets on oil coolers with success. This diesel beast is new for me.

Thank you guys for taking time to give me feedback.