My 1997 3.8 lesabre has oil in the water and excessive preasure in the radiator. Also when I remove the oil filler cap it releases air preassure. There is no water in the oil and the engine runs fine. When the oil filler cap is removed and the preassure is released the idle drops and then returnes to normal.

Help!!
dlester36

 

A leakdown test would help determine where the problem lies.
A controlled amount of air is placed under low pressure in one of the spark plug holes with that piston at the top of it's travel.
If air is heard exiting from the radiator it would most likely indicate a head gasket problem.
If it is heard from the oil fill, an internal piston or ring problem.
If heard from he intake system , an intake valve problem
If heard from the exhaust pipe , an exhaust valve problem.
Don't know how involved you want to get in this so will stop here until you decide what you might want to do.
Forgot to mention to check your trans fluid level. Since there is a trans fluid cooler located inside the radiator and that could be the source of the oil also.
Also there were problems with the intake plenum getting burned by the EGR tube passage , but that usually allowed coolant to get into the oil.

 

Commom problem I guess, found that out after the engine became liquid locked by antifreeze which I know for a fact corrodes piston walls. Poor design on GM's part. I was told by the mechanic that the new part was upgraded so as not to have the same issue. The upper intake manifold had to be replaced and cost $636.