With a minimum knowledge of car engines, you can put a new thermostat in your own car. However, you should be careful to prevent damage to the thermostat housing, since many are made out of aluminum or plastic. Also, be careful as you clean the sealing mating surfaces from gasket material. A small damage here can lead to a leak later on.
Park your car in a safe place and open the hood. Make sure the engine is cool enough to the touch to avoid spraying hot or boiling coolant as you remove the thermostat housing.
Locate the thermostat housing. You will find it on top or on the side of the engine by following the upper radiator hose. The hose fitting is part of the thermostat housing.
Place a drain pan underneath the engine, in the direction of the thermostat housing, to catch the coolant from the radiator hose as you remove it from the engine. Then remove the two or three mounting bolts from the thermostat housing using a wrench or ratchet and socket.
Tap the thermostat housing lightly using a rubber hammer to free the housing from the engine if necessary and lift if off the engine. Remove the thermostat from its housing.
Scarp old gasket material from the seal surfaces on the thermostat housing and engine if necessary. Use a plastic scraper to avoid damage to the surface.
Place a small glass or mirror against the sealing surface of the thermostat housing to check for wrapping. If necessary, file or sand the sealing surface flat.
Sit the new thermostat in place with the spring pointing towards the engine. Apply a light coat of gasket sealer to the new thermostat gasket and install it on the engine sealing surface. Some thermostats use a rubber seal instead of a gasket. Make sure the seal sits properly in its groove and stays in place as you install the thermostat housing.
Start the mounting bolts by hand and tighten them with a wrench or ratchet and socket. Be careful not to over tighten the bolts to avoid damage to the threads and thermostat housing.
Start the engine and let it reach operating temperature. Check the reservoir coolant level and add as necessary to bring it up to the "Full Hot" mark.
