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oil in radiator - Vortec 5.3 LM7


Topic starter


I have Chevy Express 2007 AWD with Vortec 5.3 LM7 engine. I have found oil in coolant - milky stuff below radiator cap. I discovered that mix oil-coolant comes from little tubing which goes from the engine head to top of the radiator. I dont see any coolant in engine oil. I didnt experience overheating, engine codes or excesive or low oil pressure. Nothing. Van was driving OK - I guess I just have found it before it could make a mess.

My question is what could be the issue:

1/ transmisiion cooler - maybe it is transmission oil in coolant but why I see oil/coolant mixure enetering from the tubing which goes from cylinder head?

2/ blown head gasket - how to verify that? I did combustion leak test (suck air from top of radiator and checking if testing fluid goes from blue to yellow) with negative result. Seems the head gasket is not blown in cylinder area. Could be head gasket blown in oil passage only letting oil to enter coolant? How can I verify that without removing the engine head?

Thanks for any opinions/advice.

3 Answers

These engines don't leak oil from the head gasket. ( might be a Japanese thing?).


Are you absolutely sure it's oil and not something else like stop-leak? Dexcool can start to get sludgy if you don't change it for a very long time, or it gets mixed with something else.


If it is oil, then the engine oil cooler is a heat exchanger located inside the left side end tank of the radiator . That would be the most likely oil leak culprit. (ATF would be in right tank if installed)


There's no other place oil + coolant could mix. If the schmutz floats on water, that might be why you see it coming from the coolant air bleed pipe. (highest point).




Coolant was pretty clean. I bought this car recently - no signs of anything duringinspection before purchase.


I see transmission cooler lines coming to the radiator but no engine oil cooler lines going to radiator. There is no engine oil cooling inside radiator on my car. I belive that was the case for vortec 6.0.


You say, there is no other place where coolant and engine oil meets? I bet it is transmission cooler then - or some residue after flush.


I am assuming its oil because looks like milky sludge which has white or pinkish color - I guess it gets color more after dexcoolt than after oil. My transmission fluid is dirty - clearly hasn been changed for years, engine oil normal. Not sure if the oil color can say something about the color of the mixture


I hope you don't mind if I post your photo from chevroletforum. It helps for diagnosis.


the Strawberry Milkshake of Death

If water gets into the transmission then I'm afraid its days are numbered.

I just found it right away - maybe three days ago when it started. I guess if there was just litle water and it is not very mixed - I can just flush it and it should be OK.

definitely do a flush, but drop the pan and replace filter too.

Topic starter

but the head gasket of vortec 5.3 LM7 looks different that on e on your picture though. Can be seen here,5412 or on the picture below. There is place where engine oil can leak into the coolant. Still very unlikely though. I'll check that tranny cooler and hope that is the case.