General Motors has produced a 3.1-liter engine since 1993, when they released the 3.1/3100 engine. Since then, General Motors has offered the 3.1 as an option on most vehicles, including the Chevy Malibu. The thermostat on the 3.1-liter engine rests inside the water outlet housing, which connects the upper radiator hose to the engine. This makes it straightforward to replace, because the housing is right out in the open for you to reach.
Locate the water outlet housing by following the upper radiator hose to the location where it secures to the motor. The hose clamps onto the lid of the water outlet housing.
Remove the bolts that secure lid of the water outlet housing to the bottom half of the housing with a socket and ratchet. Lift the lid off the housing to expose the thermostat.
Pull the old thermostat out of the housing and replace it with a new one. The end with the spring on it rests inside the lower half of the housing.
Lift the old gasket off the lower half of the housing and wipe the mating surface of the housing clean with a towel. Wipe the mating surface of the housing lid clean as well.
Place a new gasket onto the lower half of the housing, place the lid on top of the gasket and thread the bolts back onto the housing with your fingers. Tighten the bolts with the socket and ratchet.
