1997 Toyota Corolla Change a Thermostat
The thermostat in the 1997 Toyota Corolla uses a valve filled with mercury to measure the engine temperature. As the coolant in the engine reaches 190-degrees Fahrenheit, the spring inside the thermostat compresses. This allows an increased amount of fluid into the engine, thus lowering the engine temperature. When the thermostat fails to work properly, the engine could overheat if it fails in the closed position. If it fails in the open position, the engine could fail to reach proper operating temperature and run too cool.
 Tools Used
 Change a Thermostat
- Place a drain pan under the petcock on the bottom of the radiator. Open the petcock with a pair of pliers and drain the contents of the radiator into the drain pan. Close the petcock once finished.
- Trace the lower radiator hose to the engine. The hose connects to the water inlet housing on the water pump. The inlet housing is a small, dome-shaped cover with a small metal tube protruding from it to which the lower radiator hose connects. The thermostat resides inside the water inlet.
- Pry the radiator hose clamp off the hose with a pair of pliers and pull the hose off the inlet.
- Remove the two nuts that secure the water inlet onto the water pump with a socket and ratchet.
- Pull the water inlet off the water pump. The gasket that fits onto the thermostat holds the thermostat inside the water pump.
- Note the location of the thermostat inside the pump. Use the studs that you removed the nuts from as location references. The top of the thermostat has an arrow on it and that arrow points between those two studs. The arrow on the replacement thermostat must be in the same spot.
- Pull the thermostat out of the water pump.
- Place the new O-Ring gasket onto the thermostat. The O-ring has a small groove on the inside diameter. This groove fits around the circular housing on the thermostat. Use the old one as a reference for how this should look.
- Place the thermostat into the water pump. Again, make sure it orientates correctly.
- Place the inlet housing back onto the water pump, thread the two nuts back onto the threaded studs with your fingers and then tighten the nuts in place with the socket and ratchet.
- Slide the lower radiator hose to the inlet housing and secure the clamp to the hose with the pliers.
- Push down on the radiator cap located on the top of the radiator and turn it counterclockwise to remove it. Place a funnel into the filler spout and drain the coolant back into the radiator. Close the cap once finished.