Re: petcock valve at the rear of the intake manifold.

["ambradley@frontiernet.net" <ambradley@frontiernet.net>]

That is for flow into the heater core.  Don't recall which direction is
which, but it shouldn't cause the car to overheat either way.  If your
car has a LOT of air coming out the cooling system, you likely have a
head gasket leak, allowing exhaust into the cooling system.  It was so
bad on my car that it sounded like an air horn.