Were is the thermostat located in a Pontiac Sunfire 2000?

Hi:
Your thermostat is located under the thermostat housing, which is what the upper radiator hose clamps to on the top of your engine. Basically, you need to start with a cold engine, drain your radiator, then unclamp the upper radiator hose from the engine. Remove the bolts from the thermostat housing, and gently tap on it to remove it. clean up the mounting surfaces on both the engine and the housing, and install a new thermostat, and new gasket. tighten to proper torque, reconnect the radiator hose, then refill up the radiator and cooling system.