Jim Grant's Tech Tips
'98 Pontiac Grandprix, Intake Trouble
Q: Two days ago I changed
both lower intake gaskets on my 98 Pontiac Grandprix 3.8 with 86k.
The drivers side was leaking antifreeze. After I reinstalled everything.
I started my vehicle and it ran fine and sounded good too. But when I
pulled the oil cap off while it was running to check for any internal
anti freeze leaks, the car had a high vacuum pressure as if it didnt
want the cap to come off. The same thing happened when I pulled the dip
stick too. The engines idle changed, the car started purging for
air, then when I drove it gave off this loud awful screeching sound, off
and on while driving............please tell me what you think it could
I would suggest going back down to the parts store and picking up another
intake manifold gasket set and get set-up to change the intake gasket
set again. Why? Either you damaged or incorrectly installed the gasket.
Having such a great volume of engine vacuum in the crankcase is a sure
sign of an internal leak. The intake manifold gasket on your vehicles
engine seals the intake passages. If there is a leak due to damage or
use of the incorrect gaskets a vacuum leak will occur. In your case the
leak is into the internals of the engine. Dont drive your vehicle
under this condition. Having a vacuum leak of that size into the engine
will cause oil consumption and could damage other gaskets and seals.