A broken thermostat in your car may cause the engine to overheat or remain under operating temperature most of the time; either way, it can cause severe engine damage. Yet, a thermostat is a simple component you can remove and install yourself.
Park your car in a safe place with enough room for you to work around the front of your vehicle.
Open the hood and locate the thermostat. Follow the large, upper radiator hose towards the engine. The hose is connected to the thermostat housing, attached to the engine by two or three mounting bolts on top or to the side of the engine.
Unplug the temperature sensor wire from the thermostat housing if your particular model comes equipped with it. Press the lock tab on the plastic connector and separate the wire connector.
Place a drain pan underneath the vehicle, on the direction of the thermostat housing. Remove the clamp holding the upper radiator hose to the thermostat housing using slip joint pliers, standard screwdriver, Phillip screwdriver or ratchet and socket, depending on clamp type used on your particular model; then detach the hose from the thermostat housing.
Unscrew the thermostat housing mounting bolts using a wrench or ratchet and socket; then remove the thermostat housing and thermostat. If the thermostat housing is stuck to the engine, tap it with a rubber or plastic hammer. Remove old gasket material off the thermostat housing and mounting surface on the engine using a plastic scraper to avoid damage to the mating surfaces.
Place the new thermostat in place with the spring pointing towards the engine. Make sure the unit sits properly. Install the gasket or rubber seal. On some vehicle models, a sealer compound is necessary when installing this gasket. Consult your car owner's manual or ask your auto parts salesperson.
Install the thermostat housing and start the mounting bolts by hand. Tighten the bolts using a wrench or ratchet and socket but make sure not to over tighten them to avoid damage to the threads or thermostat housing.
Connect the upper radiator hose to the thermostat housing and install the clamp; then plug the temperature sensor wire. Add a mixture of 50 percent antifreeze and 50 percent water to the radiator to bring coolant to the proper level. Install the radiator cap or reservoir lid. Start the engine and check for leaks. If you used sealer compound on the thermostat gasket, follow the product manufacturer instructions to allow the compound to dry completely before operating the engine.
