Q: Engine overheating "still" after intake manifold gasket & thermostat replaced on 1998 Oldsmobile Silhouette

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Water temp gauge began running hot. Replaced intake manifold gasket. Slight trace on coolant in topend. Also replaced thermostat and flushed coolant and replace. Water pump not leaking. Replace fuel filter, plugs/wires, serp belt, air filter. Engine runs great, but temp gauge going into the red. Radiator cap cold, but engine dangerously hot. Tech thinks air may be getting into coolant system causing a cavatation. Need help.
(1) Answer
First, scan the coolant temperature sensor to make sure the engine is really running hot, if the radiator is cold, that is puzzling, because it should hurt your hand to just touch it, if the engine temp gauge is in the red on a hot running GM car, it will read at least 225 degrees or more on a hot running engine. Then if that checks out ok, then do a BLOCK CHECK, this is a chemical test of the coolant to make SURE that there are no exhaust gases getting into the coolant. If there are then you most likely have a head gasket problem.