Pontiac Repair: 1995 Pontiac Bonneville 3.8 engine, coolant leaks, intake manifold gasket

Question
I get a squealing sound from the engine after it
runs for about 5 minutes, sounds like a belt noise
If I take the oil fill cap off, the noise goes
away but engine runs terrible, like a vacumm leak.
When I put my hand over the fill hole it gets
sucked tight and the engine smooths out. Ive heard this engine had some manifold problems, but
I thought they pertained to coolant leaks. The
squaling noise I'm hearing sounds like it is coming from the rear of the motor down by the exhaust. Ever heard of this problem? Thanks for your time

Answer
It is normal to have a slight suction from the oil cap due to the PCV valve. If it has enough suction to suck your hand tight, it probably has an internal vacuum leak. If the intake manifold gasket is cracked it can let intake vacuum leak into the crankcase.
Yes, there are some problems with the upper intake manifold burning through at the EGR tube opening and causing the coolant to leak into the top end, but this is not your problem. At least for right now.