Coolant in oil (Oil analysis)

[Hammerhead]

(05-27-2017 )jorden486 Wrote:  Usually oil cooler issues are oil in the coolant because the oil runs at higher PSI so it pushes oil in the cooling system while the truck is running and some coolant will leak back into the oil system when the truck is shut off.

Agreed.
However, occaisionally things don't always play out in a linear manner.
I had a liquid tranny cooler fail several years ago sending oil into the coolant. Everybody said it was the engine oil cooler that failed. There was no way a transmission cooler would create enough oil pressure to overcome the cooling system pressure to push tranny oil into the coolant, never mind the fact that it also has to overcome gravity.
The color of the oil emulsion was wrong, and I just couldn't put that suspicion out of my head. I sent oil emulsion samples as well as oil samples from the; engine, tranny, & APU for analysis and elimination. The emulsion from the surge tank matched the tranny oil additives only. The tranny oil contamination was so slight, that had I not have sent in the emulsion sample and clearly explained what I was looking for, they may not have found it. They doubled the tranny oil sample for verification.
All this means is that Most of the time this is the case, however never presume that sometimes things just may not be what they appear.

Based on all of this, I would actually rate the air compressor as a higher likely source than the oil cooler. However I have never heard of any way to test the compressor short of replacement, which was why I indicated the oil cooler ahead of the compressor. (Unless the air drier dessicant is obviously contaminated with coolant) The oil cooler can be pressure tested when removed for confirmation or elimination.

Personally, I suspect EGR cooler. They seem to have the highest failure rate.