The thermostat in a Buick motor is a valve that controls the flow of water between the engine and radiator. When you first start your car, the thermostat is closed, blocking coolant from the radiator and allowing the engine to heat up to normal operating temperature quickly. Once normal temperature is reached, the thermostat opens and allows coolant to circulate through the engine. A stuck thermostat is a common cause of overheating, and should be replaced immediately to prevent damage to the engine.
If you are concerned that your thermostat is malfunctioning, check a few things before replacing it. Check the coolant level in the radiator, but make sure the engine has completely cooled down before doing so. Also check the tension on the water pump drive belt. Place a straight edge against the water pump and crankshaft pulleys and then press down on the belt.
Measure the distance between the belt and the straight edge. It should be no more than 1/4 to 1/2 inch. Next turn on the engine. If it takes a long time to heat up, the thermostat is most likely stuck in the open position. If the engine is running too hot, carefully place your hand on the upper radiator hose. If the hose is not hot while the engine is, the thermostat is most likely stuck in the closed position.
Wait until the engine has completely cooled off and begin by draining the cooling system. Locate the petcock valve on the lower corner of the radiator. Place a waste oil collection pan underneath the valve and open it. Next, locate the thermostat housing; it will be mounted to the intake manifold and connected to the upper radiator hose. Remove the upper radiator hose by loosening the hose clamp and pulling the hose off the housing. Then remove the bolts that connect the thermostat housing to the intake manifold. Once you remove the housing you can simply lift the thermostat out of the intake manifold. Note the position of the thermostat before removing it.
Clean the gasket material off both the intake manifold mounting surface and the thermostat housing, using a razor blade. Drop the new thermostat into position. Then apply a thin coat of gasket sealant to both sides of the new gasket and place it in position on the intake manifold. Reinstall the housing over the thermostat and reinstall the two bolts that connect it to the intake manifold. Reconnect the upper radiator hose to the housing and tighten the hose clamp. Lastly, fill the radiator with fresh coolant.
