LBZ: Oil in Coolant

[cactuscat]

Hello everybody. I need some assistance with diagnosing coolant/oil cross contamination. So after coming back from a long trip in the lbz, I noticed during regular service that the engine oil was just a tad little low. After some further inspection, I found a layer of black oil in the coolant reservoir. Initially I thought it was atf, but the oil was charcoal black. I checked the oil, and it’s pitch black with no signs of coolant. There is oil in the coolant, but no coolant in the oil. I started thinking it might be a headgasket, but there is no coolant loss, and the hoses aren’t hard after sitting a while. I pressure tested the system at 15psi for an hour, and it leaked down 2 psi. I pressure tested it with the oil filter off to see if maybe it was leaking thru the oil cooler, but I couldn’t see any leaks. At this point, I’m starting to leaning toward a bad oil cooler. I know oil pressure is higher than the cooling system pressure, but with the cooling system only dropping 2 psi in an hour has me baffled. Maybe it only leaks oil into the cooling system at 30-40psi? Any help is greatly appreciated

 

[Ridin'GMC]

The oil cooler usually leaks when the engine is hot which will open up the crack.

 

[torqued2dmax]

Could a gasket in oil cooler be leaking in to the coolant ?

 

[Dozerboy]

How long have you had this truck? It's normal for the oil to be low because of the PCV. What do you mean black oil in the coolant? Is it floating in the coolant or is it collecting on the walls of the reservoir?

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[cactuscat]

How long have you had this truck? It's normal for the oil to be low because of the PCV. What do you mean black oil in the coolant? Is it floating in the coolant or is it collecting on the walls of the reservoir?

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I’ve had it about 2 years now. 205k on the clock. It’s both. There’s a layer of black oil floating on top, when I pulled the hoses going to it, there is a layer of brown sludge coating the inside of the hoses. I know the hoses weren’t that way before because I had replaced the entire bottom hose last year.

 

[cactuscat]

The oil cooler usually leaks when the engine is hot which will open up the crack.

Could a gasket in oil cooler be leaking in to the coolant ?

Maybe there’s a crack in the plates inside the cooler? Or maybe oil is seeping past an o ring or something? It’s the only thing I can think of, so I’ve got a new cooler and gaskets on the way. I’ll update after I get it swapped out

 

[Wsmith13]

Did you ever figure out the problem? Mine is a 06 lbz having the same issue. I've done head gaskets, head studs all top end gaskets. Crankcase oil is clean and clear and the oil in reservoir is black. Engine is running great. New water pump. I put new gaskets in the oil cooler when putting Engine back together. Any help would be greatly appreciated!

 

[Justmikedmax]

Same boat here ,snapped crank in my lbz and have just purchased a salvage motor with 130k upon cleaning it up and replacing all top end gaskets prior to install I have found oil in the thermostat housing and crossover pipes ,where they meet the heads . Motor has head studs and new grade c gaskets so at some point it had bad head gaskets and prior to me they were replaced . Really don’t wanna shove it back in and have to pull it again for head gaskets . Oil cooler leak possibly ?? Any info would be greatly appreciate as I’m planning to slide her in the truck this weekend . Thanks

 

[LBZ]

I’d start with a new cooler and a good system flush. 9/10 times the cooler is the culprit.