Car overheating, blowned head gasket or closed thermostat

Try taking out your thermosta and boiling it in water on the stove. It should open before the water starts boiling. If it dont, replace it. If it does then one of two things could be at fault. One your water pump may be bad. There are a few ways to check this. One is to replace the thermostat and take off the cap. Run the motor until it starts to get hot. If the water pump is working you'll see the fluid in the radiator "cycling" through it(this will work if you just take the thermo out and do it too). If the fluid doesn't "cycle" then you have a bad pump. If it does, then one of two things could be happening. Your fan relays may be bad or the fans themselves may be bad. Check 'em. One is suppost to spin at like 160 degrees and the other at like 190(don't quote these numbers though). If both of your fans are working then there is only one thing left to check. Run your motor till it's getting fairly close to redline temp(at least hot enuff that the top of the radator is hot). Turn the car off and put your hand at the bottom of the radiator and see if it is hot also, if it is not then your radiator is most likely clogged up at the bottom. Cleaning it would be almost a much as replacing it with an aftermarket radiator. If it is none of the above then maybe just your gauge is botched.

I have a 94 Trans Am with the same problem and it turned out to be the radiator is bad.I haven't replaced it yet(thats for tommorrow!) So I'm only 95% sure thats what's causing me to over heat.I'll let ya know if a new radiator that'll fix it.