akuhr

Hey there Folks. I have an '05 C55 with about 155,000 miles on it. I have owned the vehicle for a little over 2 years now and love it. However, ever since I've owned the vehicle I have had to top off the coolant occasionally. In the summer time, it is worse than in the winter, and it is definitely worse when doing city driving. I recently submitted an oil analysis to Blackstone to see if it may be mixing with the oil (I did not see any milky or cloudiness in the oil so I was very curious what was going on with the coolant), and they said the coolant is mixing in with the oil (guess that's why I could never find a visual coolant leak!). I replaced the oil cooler about a year ago, since I noticed it was leaking. I have also replaced the radiator with the newer version (preventative). There is not any oil in my coolant.

Anyone have any ideas what may be going on or recommended next steps?



Thank You all for your help and input.

MattCordell

The C32 had bad Valeo rads from start which caused coolant leak into the transmission oil and caused tranny issues.
Transmission was damaged from this.

The C55 should have a better radiator than C32 from when the car was new, when you replaced radiator you probably bought a new Behr from dealership?
You might have the same leak as with the C32 cars, coolant mix with oil

akuhr

Hey Matt. Yep, that is correct, it is a Behr unit. FCP Euro also has a Nissens kit, and I see on some other sites you can find a Valeo one. I guess I did not look beyond the site reviews before buying it, which looked pretty good. Maybe getting the Behr one was a mistake.

MattCordell

Behr made in Germany is the very best.
Behr made in China is not so good!
If you bought the correct one you don't have to worry a thing.

C55 shouldn't have the same issues C32 had with coolant leaks into transmission oil.
MB should have fixed this design flaw not fitting inferior parts?
Perhaps they didn't?

alb3rtt

Your radiator would not cause engine oil and coolant to mix, only transmission oil and coolant.

C55s are safe radiator wise, so are Valeo's newer than late 2003.

Freak failures can occur given the nature of the radiator design, but it is not a widespread issue.

Your oil cooler on the other hand can definitely cause engine oil and coolant to mix if it is leaking internally.

That being said, you should be able to see coolant in your oil if that was the case unless it was very minor.

brauhaus313

Yeah, way off base on suggesting a bad radiator can cause coolant to get into the engine oil on your C55.

Bad headgasket and internally leaking oil cooler would be where I would look first.

duke749

2 O-ring seals between timing chain cover and engine block can leak . check out .. Tosos Moschatos you tube channel he just did a repair on a E55 with 138k on clock
with this fault .. he,s done about 5 videos on the repair in the last 2 weeks ... I have a nissen radiator in my C55 with 30k km on it and 5 years old no problems