Why is there A light brown oily gunk in the radiator?
Thick light brown oily gunk mixed in with
antifreeze. Did pressure test on radiator, Held
pressure fine. No leaks anywhere. Head gasket, is
ok. No crack in block. Has no oil cooler so it can't
be that. But tranny oil cooler is built into the
radiator I'm told. PLEASE HELP!! WHAT DO I TRY
Sometimes dexcool antifreeze can get that foamy looking stuff in it, if air gets into the system. Also, Your oil pressure is usually higher than the pressure cap on cooling system, so you would get oil into cooling system before coolant into oil, just my opinion. Is there any coolant in your oil? There is nothing that says the tranny lines in radiator can't corrode, If you think the leak is transmission fluid. I'm just thinking out loud, good luck.
YOU MAY HAVE AN OIL LINE LEAKING INTO RADIATOR LINES OR TRANSMISSION LINE. ALL ABOUT TROUBLE SHOOTING.