Oil still mixing with coolant even after replacing head gaskets - Mercedes-Benz Forum
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post #1 of 22 (permalink) Old 07-10-2019, 01:47 AM Thread Starter
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Oil still mixing with coolant even after replacing head gaskets

Hi I have a 1979 450 SLC with 77k miles. I have oil mixing into the coolant and some coolant mixing into the oil. I have replaced both head gaskets and have had the heads machined, yet this problem persists. Any thoughts/ideas to resolve this problem would be much appreciated. This was the sequence of events:

1) Car overheated due to a blown upper radiator hose. Replaced upper and lower radiator hoses, added coolant. Car ran well for 500 miles.

2) Noticed oil in the coolant overflow tank. Flushed coolant system several times, replaced coolant. Drained oil, no coolant in oil, replaced oil. Drove for 20 miles.

3) Oil present again in the coolant overflow tank, and now some coolant mixed into the oil. Engine was not misfiring and ran on all 8 cylinders

4) Removed driver and passenger heads. Valve job to both heads, pressure tested (no cracks), surface. Cleaned intake manifold. New head and intake gaskets. Radiator was rodded, cleaned, pressure tested. Almost all hoses were replaced. Followed all the instruction meticulously from the MBZ 117 engine manual. The block was not removed from the car. No visible cracks on the cylinder walls. No signs of damage to the surface of the block. Torqued all the bolts and tested three times.

5) Car started on first try, ran very well, did not overheat. Flushed the fluids multiple times. No coolant in oil or vice versa. Drove 50 miles with no issues. Parked car for 5 days and upon return noticed oil in coolant. Flushed the coolant again, drove 10 miles, same result. Oil in coolant and coolant in oil. I have lost about 2/3 of a quart of oil into the coolant system since the last flush.

I am guessing that maybe it could be the O-rings between the timing cover and the block behind the water pump?? but would like more opinions before I start taking things apart again. Have any of you had a similar problem with your 450?

Thanks
OC450
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post #2 of 22 (permalink) Old 07-10-2019, 02:02 AM
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oc450 sorry to hear about this .Its hard enough striping it down to replace the head gaskets . And then to find out that you still have the problem . It looks like waiting to see what answers come up from other forum members .
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post #3 of 22 (permalink) Old 07-10-2019, 07:36 AM
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I have no answer for you but I find it strange that oil would be in the coolant tank and coolant in the oil. I would expect it to be one or the other but not both.

You say you are loosing oil... I believe you said 2/3rds of a quart. Was there 2/3rds of a quart or oil in the overflow tank? If not... where did it go? Oil floats on water so it should eventually find it's way to the highest point.

Is it possible that you have two different issues?

Any possibility of a hose or tube being connected to the wrong place or perhaps left off?

Do any of the head bolts pierce a water jacket? Pipe joint compound?

Just thinking out loud.

Good luck.

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post #4 of 22 (permalink) Old 07-10-2019, 10:26 AM
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After all that work, not fixed I am sorry you are having such a vexing issue.

When you wrote "surface," did you mean that the heads and block mating surfaces were machined flat?

Please let us know when a solution is found. Best wishes!

John
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post #5 of 22 (permalink) Old 07-10-2019, 12:36 PM
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There is probably a common path somewhere between the oil and coolant (head gasket, cracked block, cracked head, warped head and/or warped block surface). When the engine is running the oil press (50 to 60 psi) can overcome the coolant pressure ~15 psi. When the car is off the residual coolant pressure overcomes the oil pressure (0 psi). Hence oil in coolant and coolant in oil.

Did you use OEM MB gaskets?
Any white smoke when the car is running?
Did you check the flatness of the block surface for with the heads removed?
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post #6 of 22 (permalink) Old 07-10-2019, 03:20 PM
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I had that problem once when I failed to torque the intake manifold bolts properly
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post #7 of 22 (permalink) Old 07-11-2019, 02:21 AM Thread Starter
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Hi Jyuma - Yes, most of the oil is ending up in the coolant overflow tank. The remainder seems to be at the top of the radiator and inside the block before it makes its way to that overflow tank. All the hoses seemed to be connected properly.

That's a good point of there potentially being two separate issues instead of only one. I had assumed that there would be only location where "cross contamination" is occurring
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post #8 of 22 (permalink) Old 07-11-2019, 02:40 AM Thread Starter
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Originally Posted by jsebastian View Post
After all that work, not fixed I am sorry you are having such a vexing issue.

When you wrote "surface," did you mean that the heads and block mating surfaces were machined flat?

Please let us know when a solution is found. Best wishes!
Hi jsebastian - Indeed it was very jarring to see the "milkshake" of coolant and oil after having spent so much time taking things apart and reassembling.

Yes, by surface I meant that the surface of the head was machined flat. I did not remove the block from the car, so all I did was remove any residual head gasket material (very carefully), cleaned the surface of the block with acetone, and checked for straightness. There was no corrosion or low spots on the block. The head had some corrosion, but almost all of it was removed during the machining
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post #9 of 22 (permalink) Old 07-11-2019, 03:22 AM
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Unfortunately all I can think of is the timing chain cover and a crack in the head or engine block at the point where oil comes up to lube the head. Unfortunately I cant think of any reasonable way to test without taking stuff apart.
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post #10 of 22 (permalink) Old 07-11-2019, 03:28 AM
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You did not mention overheating as being concurrent with the oil/coolant, coolant/oil cross contamination, which suggests we can rule out head gasket issues. That leaves intake manifold and timing chain cover.

I believe the water pump bolts through the timing chain cover and into the block. Given all you have already done, that is the next place I would look.

Good luck.

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