I have a 1996 Blazer 4.3L 4WD. I found oil in my radiator and overflow bottle. I checked the oil and there is no coolant in the oil. As I understand it there are three likely causes: blown head gasket, intake manifold gasket, or oil cooling line inside the radiator leaking. I got a combustion leak test and the results are negative for combustion gases in the coolant. That rules out the blown head gasket. How can I test if the problem is the intake manifold gasket or the oil cooling system in the radiator?

Right now I disconnected the oil cooling lines from the radiator and pressurized the radiator to see if I could get the coolant to leak out of the oil cooling line holes, but so far no coolant has leaked out of the openings.

I appreciate any help. Thanks. Mark.

 

I think you are close to your problem, I had this problem and it was the intake gasket, some how this is a common problem on 4.3 v6, you will probably find the drivers side is where the leak is, I when ahead and replace both side. Hope this helps you.

 

I have a 4.3 L V6. Around 90,000 miles i had the same problem. It was the intake manifold gasket. Had it changed 3 years ago.