2001 pontiac gran prix gtp

Classic GP problems ,, First look on the engine block directly across from the radiator and you will see 2-very small hex head screws (one on each side ,, follow the big hoses for locations) loosen the screws until they are almost out ... fill the radiator with coolant until the screws are leaking solid coolant ,, (air is purged from engine) the tighten (snug not balls to the wall) ,, next and this is not trivial but extremely important ... make absolutely positively the radiator cap is tight ,, if you can wiggle it then it's not sealing ,, it must hold pressure because water can't boil under pressure,,,, next make sure that your radiator fan works

Evidently if your trying to seal a head gasket with a mechanic from a can it's not working so fix the real problem Get a real mechanic