Help! Oil in Coolant - But no Coolant in Oil ?!?!

[heathcliffe]

Need some help. Just finished a B35 swap (with the invaluable aid of yert315 :thanks: ) . Car is running great but then I noticed oil in the coolant tank. I was hoping it was some residual that got in during the motor build so flushed coolant and prayed. More oil in coolant. No sludge or coolant on oil filler cap or on dipstick. No overheating. Oil looks as pristine as it should on a motor with less than 200 miles on it. Pulled the head to check head gasket. Everything looked great. No leaks or damage but replaced anyway with an Elring head gasket rather than another Victor Reinz HG. And...still getting oil in coolant!!
At wits end. Where could oil get into the coolant without the reverse happening? The car runs great. No overheating. Not getting any smoke/ steam out of tailpipe. Doesn't seem to really be losing either oil or coolant. Where can the contamination be coming from? Is there any area around the water pump gasket perhaps? Any input appreciated

[TJC1]

This could be a toughie. You have oil getting into the cooling system and you are certain that the head gasket is okay and (I'm assuming) that there are no external leaks.

Does this car have an automatic transmission?
If so, was the radiator repaired recently?
Does the oil contaminated coolant have any unusual scent?
How badly is it contaminated?
Are you absolutely certain that there is no coolant getting into the oil?
Is there still pressure in the cooling system when the engine is hot and shut off? Please check this carefully.

[heathcliffe]

Thanks for help. Here's some answers point by point.
No external oil leaks that can seen.
5 Spd manual.
Radiator is almost brand new OEM.
Smells a bit oily I guess but not unusually so considering its contaminated.
It comes out reasonably clean from the radiator drain plug . As the oil is lighter it seems to concentrate in the coolant tank- high point in the system. Hard to tell as it gets pretty frothy when the motor gets warm.
I haven't done any scientific testing to confirm, but the oil looks really clean- only @ 250 miles on new motor. Usually if there is coolant/water in oil you get thick froth and/or steam out exhaust right?
Cooling system maintains pressure after shut off insofar as you will get pressure on the overflow tank until the coolant has cooled down from operating temps

[ozibimmer]

Get a Head test done . When I was building my race car I noticed oil in the reservoir, So I took the car and had it computer checked for leaks and if a crack in the head or blown head gasket. It was such a relief to find out all was good and it was just oil had somehow got into the reservoir during the build. I hope your as lucky as me. It will give you piece of mind to find out for sure.
Good luck with your car.

[dm635]

I had the exact opposite problem so this wont help you. Was getting coolant in the oil.

How you might ask? I just so happened to pull the valve cover while hot and under pressure and saw coolant dripping into the head from the top of a head bolt. Not the very top of the head bolt but at the clamping surface. Pulled head and noticed some very small spider cracking where the block surface meets the head. I'd had enough of dumping $$$$ into that M10 powered 318i and it was time to move that car on.

A problem that took a while to figure out after finding it started to wear on the cam. Knew it was using coolant, but where? Only spotted after pulling valve cover with cooling system under pressure. Only mentioning this because of its strange nature.

[TJC1]

Generally speaking the only time you would get "smoke" etc. out of the tailpipe is when coolant and/or oil is being burned in the combustion chamber which is usually indicative of a blown head gasket, cracked head or cracked block. Since this doesn't seem to be happening in your case perhaps we can rule that out for now.

When the engine is running oil pressure is greater than cooling system pressure and therefore may contaminate it but it is a somewhat freak condition. For this to happen there needs to be a pathway from an oil galley to the cooling system and that may be caused from a hairline crack, head gasket failure (even very minute, almost invisible to the naked eye) or some other occurance. I have seen a situation wherein blind head bolt holes had contamination in the bottom of them and even though the headbolts can be torqued down to spec, the contamination (could be oil, coolant, etc.) actually creates a "Hydraulic" condition and then the seal between the head, head gasket and block is compromised.

[pthm]

the frothy bit I have had on an M10. Why mine did was because the water galleys had been exposed to air long enough to have a fine surface rust and it contaminated the coolant and frothed

[Flash635]

I'm putting my money on a pocket of oil somewhere in the cooling system that isn't being flushed out.
Have you done a detergent power flush?

[heathcliffe]

I'm putting my money on a pocket of oil somewhere in the cooling system that isn't being flushed out.
Have you done a detergent power flush?
I haven't done a power flush. I've been suspicious that perhaps something like that was going on, but wasn't sure if that was possible. Is there some system for either using high pressure or vacuum to evacuate any residual contaminants in the system rather than just running fluid through and draining it?

[PJs e32]

I have seen oil in cooling system a couple of times, one is through a cracked head, from an oil gallery to a water gallery, I would do a detergent power flush, and then recheck. If it continues I would get the head checked for cracks, focusing on oil galleries. As coolant is usually under pressure, it usually has to come from somewhere that has a higher pressure to get into the system.