The 2003 Pontiac Grand prix uses a mechanical thermostat designed to increase the flow of radiator coolant through the engine when the temperature of the coolant surpasses 180 degrees. The thermostat prevents the engine from overheating. If the thermostat stops working, the design allows it to fail in a save position that allows fluid to flow unrestricted through the engine. This prevents overheating, but it also prevents the engine from producing enough heat to warm up the inside of the vehicle. When the thermostat breaks, replacement is the only option to correct the issue.
Drain approximately 2 gallons of coolant into a clean drainage pan from the petcock located on the bottom of the radiator. You will reuse the coolant.
Follow the upper radiator hose from the radiator on the Grand Prix to the intake manifold, where the hose connects to the water outlet housing. The thermostat rests inside the water outlet housing.
Clean any debris away from the outlet housing with a towel or compressed air. It is common for leaves and other road dirt to build up around this area. A clean surface prevents any contaminants from getting into the cooling system.
Remove the two bolts that secure the water outlet housing to the intake manifold on the Grand Prix with a socket and ratchet. Lift the housing off the intake manifold to expose the thermostat.
Lift the old thermostat out of the intake manifold and shove a shop towel into the newly exposed hole.
Scrape the old gasket off the surface of the intake manifold with a metal scraper or small wire brush. Do the same with the bottom of the water outlet housing.
Remove the shop towel from the hole in the intake manifold and place the new thermostat into the hole. The end with the spring goes into the hole while the end with the pin sticks out.
Place a new gasket over the thermostat and place the water outlet housing on top of the gasket. Secure everything with the two bolts.
Open the lid on the radiator expansion tank and drain the 2 gallons of fluid back into the radiator.
