W204 C220 CDI Auto - oil at the top of the engine in the holes adjacent to the injectors - see photos

[Titansilver]

I am having an issue with our 2014 W204 C220 CDi Auto that has covered 173k miles.
Looking at the top of the OM651 engine, I can see some liquid in the holes adjacent to the injectors.
See attached 2 photos.
It's only present on the rear 3 holes.
it appears to be black engine oil.

What is the most likely cause of this? And likely cure?

Thanks in advance.

 

[w204benz]

Clean the area well and check the liquid again when it builds up.

I had a similar problem, and after I cleaned all the dirty dark liquid, the freshly leaked stuff was a lighter colour than the engine oil. It turned out to be diesel, the fuel return line was leaking from the o-ring seals.

If it is oil, I vaguely remember reading about someone with a cracked rocker cover while trying to figure out what was wrong with mine.
Injector seals were the first thing I suspected before I figured out it was diesel - I don't know if they can cause oil to pool up like that, but I had them done for good measure.

I'm sure the holes are connected, so eventually they will all fill up. But if you catch it early after cleaning everything, it should help locate the source.

 

[star]

Rocker cover gaskets go hard and intern the bolts “loosen”. The bolts might tighten up a bit but the full cure is to replace gasket.

 

[Titansilver]

Clean the area well and check the liquid again when it builds up.

I had a similar problem, and after I cleaned all the dirty dark liquid, the freshly leaked stuff was a lighter colour than the engine oil. It turned out to be diesel, the fuel return line was leaking from the o-ring seals.

If it is oil, I vaguely remember reading about someone with a cracked rocker cover while trying to figure out what was wrong with mine.
Injector seals were the first thing I suspected before I figured out it was diesel - I don't know if they can cause oil to pool up like that, but I had them done for good measure.

I'm sure the holes are connected, so eventually they will all fill up. But if you catch it early after cleaning everything, it should help locate the source.

Thanks for your reply.
That's an excellent suggestion.
Yesterday, I cleaned out all 4 holes using paper towels folded into narrow tubes.
The front hole was clear, a little bit of liquid in the second and a bit more in the rearmost two.
Hard to tell if it's dirty diesel or engine oil. It may be blackened diesel.

I'll check again in a few days and see where any new liquid appears and what type it is.

@w204benz, you mentioned the fuel return line was leaking from the o-ring seals. Would this be visible? Where would I look for this. Is it DIY-able, and any idea of the part numbers or costs required on the OM651?​

 

[Titansilver]

Rocker cover gaskets go hard and intern the bolts “loosen”. The bolts might tighten up a bit but the full cure is to replace gasket.

Thanks for replying. If it turns out to be engine oil, the rocker cover gasket could well be the culprit. I suppose I'll know in a few days/weeks.

TS

 

[w204benz]

@w204benz, you mentioned the fuel return line was leaking from the o-ring seals. Would this be visible? Where would I look for this. Is it DIY-able, and any idea of the part numbers or costs required on the OM651?

I never saw the source myself, all I know is that it was very slow. But it did help me determine that it was starting at the back - like yours.
However, I did notice that after a bit of 'spirited' driving it filled up much quicker. So if you determine it's diesel and can't see the leak, revving the engine might help.

There is a genuine MB repair section, part number A 651 070 24 32, but I believe it's around £200 from the dealers. A bit much for some fuel line and a few connectors, as apparently they are standard parts and available from diesel specialists for much less.
You may be able to get genuine MB o-rings from the dealers, if not I'm sure they are a standard size - just make sure they're resistant to diesel fuel.

DIY-able? Possibly, but probably a bit fiddly. The car was already booked in for some unrelated work, so I figured better to have someone who knows what they're doing look at it. Locating the source turned out to be the hardest part.

If you go for the MB repair section, it's definitely a DIY job, if a bit pricey.

 

[Titansilver]

I just wanted to close the loop on this issue. I had the car in with my Mercedes mechanic last week. He is confident that it is a rocker cover leak. Not a big deal , but we will get it sorted at the next major service. After cleaning, the oil takes quite a while to reappear, perhaps weeks.
Thanks to @star and @w204benz for your contribution.

TS

 

[AlanGunn]

Just looked at the job on yt.
They could have made the cover so that it came out without removing the injectors.
So much pulling for what used to be a simple job years ago.