Besides head gasket there is a timing cover gasket, oil filter gasket, water pump and thermostat. I've never had the oil filter gasket off and I wonder if it has any traffic with coolant. IF coolant runs out on replacement of any of these, then that might be a candidate.

I'm just surprised that in my case an 82,000 mile engine with good cooling properties needs this. The last time this happened to me was a car I bought that had been through a radiator replacement, indicating (so I see now) overheating.

If things go well today I will spend some time on this little project...

I'm back. I couldnt drive this car knowing it was seeping oil into the coolant-- so now the head has been prepped and the head bolts are out.

Its an easy engine to work on since nothing is corroded or misplaced. You people in California take this for granted-- but here thats an exception. I credit having both body pans intact for the clean engine compartment.

Upon removing the head bolts I found that #17 bolt (way in the back on the intake side) was rusty enough to be hard to turn the whole way out. The threads are filled with something. It might be aluminum oxide? The other two way back bolts were not so nice either.

Should I worry that the new bolt wont seat properly? The rest of the bolts look used but not abused. Several of the intake side bolts look like they have seen coolant.

I am replacing them all since I didnt have time to disassemble, inspect and order accordingly.

So far the coolant on my OM601 has remained completely clean....sounds like something was leaking, but probably in extremely small amounts. Should be interesting to see what the head gasket looks like when you open it up.

__________________
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'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The w201 oil in coolant wrapup:

I changed the head gasket on this motor last week. Its took me a long time. These motors fill the engine bay completely so things that sound easy can take a long time. Nothing hard about it if you follow the manual. I ordered new head bolts and also got new fuel line clips in advance, since those usually crack.

Anyway: the gasket showed a lot of corrosion under the coolant galleys: in one place the gasket had completely eroded away. THe engine had green coolant in it when purchased and probably for a long time before that.

The engine ran great, started well, except for a small puff of smoke at first fire. There was always about five drips of oil on the floor in the morning but since there was oil all over the filter canister from a botched oil change, I didn't think too much about that. In the last 1500 mile the oil level has dropped about a pint or less.

Once the head was off, the oil leaks became apparent. It was running down the block in a place not visible with the head on, and also under the head into the coolant. The sealing rings around the pistons seemed to be pretty good.
I chased all the head bolt holes with a 10mx1.5 tap to clean them up.

I put a good quality machinists rule on the head and couldnt get a .002 feeler gauge under it anywhere so I just slapped a new gasket on (eling oem).

ANyway, all back together now-- no oil in the expansion tank, and none on the ground. It doesnt run any better since it ran great before, but Im glad I did this before things got worse. It is important to note that the head showed etching under the coolant galleys, so no more green coolant for me!