you allmost deffinetly have a blowen head gasket do a compresion test. "notorios problem on almost all turbo charged and supercharged engins"

This might be a dumb question, but did you change the coolant when you did this work?

Yes we did. We fixed it.  Thanks

what did you do to fix the problem?

I have the same car and same problem 98 grand prix GTP 3.8 l changed the head gaskets intake had a head shop check the heads and intake new thermostat and coolant tempature sensor. Still goes to RED?? is there a way to check the water pump? What else could it be?

I am curious why nobody ever changes the radiator cap first. Makes no sense to me. A $3 part that 9 times out of ten is always the problem.