Coolant in oil

[DrJosh]

I have a m20b25 (89 325is, manual transmission, 210k miles) and am looking for some advice. I have an oil pan full of coolant (not condensation). The coolant res has a very, very, light oily film. You could almost miss it is so light, but the coolant is fresh. There is no smoke coming out of the exhaust, nor are there bubbles in the coolant res while running (ran to test these two things and shut it down)

I am going to track down a coolant pressure tester as well as a compression tester and see what my results are. Is there anything else I should look for? I have the factory oil cooler but as far as I know the coolant doesn't have anything with that. Anywhere else I should check? I can't find much on coolant in oil, only the opposite. I have read random posts here and there about it likely being a cracked head as well as posts that just say "swap it". Any extra information would be greatly appreciated.

Thanks,
Josh

[flyboyx]

My money is on your head gasket unfortunately. If you have good compression on all cylinders, the likely issue is the gasket material let go between an oil and a coolant passage. I haven't seen too many cracked m20 heads. I suppose it can happen, but I would think you would really have to get it hot and shock cool it for this to happen.

Take a good look at your spark plugs when you pull them out. This can tell you a lot.

If you have to yank the head make sure you take it to a trustworthy machine shop to be checked, milled, and the valves redone.

[DrJosh]

Thank you.

I am hoping it is a head gasket. Wouldn't there be more of an oil presence in the coolant though? I was under the impression that the oil pressure was much greater than the coolant pressure. Or perhaps the gasket material broke in between a coolant passage and an oil return passage?

[flyboyx]

You mentioned oil in the coolant in your initial post? My experience is that you wind up with more mayo in the sump than anything. When you shut the engine off, the oil pressure drops to zero but the coolant stays pressurized for some time with nothing to hold it back.

Good luck. Post up your results.

[jlevie]

Coolant in the oil will form a milky emulsion and is almost always from a failed head gasket.

[DrJosh]

Thanks. I'll keep this thread updated.

Yeah there is an extremely faint trace of oil in the coolant. I wouldn't have even given it a second thought had the coolant not just been completely flushed. You wouldn't even notice unless you looked really closely. I expected to see more enter the coolant once I ran the engine. It's worth noting that I did clean the front of the block with the waterpump off, so some contaminants could have entered the system that way. Regardless I'll pressure test the system.