Only one way to find out, find someone with a good thermostat and try it out in your car.

Most important thing everyone overlooks though is is there coolant in your radiator or is it low? Also check for color smoke coming out the back of your tailpipe in your driveway and have someone follow you on the highway. No smoke = Good. Whitish/blue smoke = blown headgasket.

 

did you attempt a complete flush of teh system? its possible something is clogged up. If you have some time on your hands, remove the radiator hoses and pour clean water or coolant through the radiator. it should make an exit out teh bottom that is just as fast as you pouring it in. if its a lot slower, the radiator is clogged up. if its only slightly slower its probably just because of all the fins,core crap it has to flow through before it gets to the bottom.

if thats fine, you might wanna check the waterpump out. if it is not pumping the amount of coolant necessary to keep the system pressurized (or not at all) there is a "weeping" hole on the waterpump itself that leaks coolant. if it is indeed leaking while the motor is running, replacement is necessary, but only if you determine the radiator is perfectly fine.

although any thermostat works, the OEM ones last much longer and are much better quality.

if everything checks out and you continue to have overheating issues, bleed the system off all the air. the bleeder is jsut like the ones found on brakes. its mounted on teh front of the block right at where the upper hose connects. top off teh radiator, leave the cap off, start the motor, let it warm for a few minutes, then loosen the bleeder bolt a little. let it run (while keeping an eye on the temps, have a friend sit in the car) until only coolant is coming out of the bleeder


if that still doesn't work, post back.

 

If you can put voltage on the fan and it spins, pull the wire off the coolant switch and connect it to the body somewhere while the engine is running. If the fan turns on, it's the thermo switch. If it doesn't, it's the relay. The thermo switch is a ground switch. It grounds the circuit when it's 1) wet, 2) really hot. If your coolant level is below the switch, it will not turn on. There are 2 thermo switches. One for the gauge, one for the fan. The little one with one wire is for the fan.

If you overheat once, usually the thermostat is ****ed. It leaks the mercury out when it overheats and never opens enough when it's supposed to after that.

Fill your coolant system with the heat on full blast or you'll trap air in the heater core. Use the bleeder screw to burp all the air out and refill until ALL the air is gone or else Boyle's Law will never take affect. English: If your coolant system doesn't hold 15 PSI, you need to fix that problem before you're going to see any change in your overheating situation. Water under pressure is harder to boil.