97 - 01 Toyota Camry Thermostat / Temperature Sensor Replacement

On some very rare occasions with high mileage Camrys, the cooling system's thermostat may fail. They may lock up in either the open or close position resulting in over cooling or heating. In the last instance when a thermostat failed, the customer was complaining of no heat in the cabin. After a brief discussion, it was learned that the temperature gauge needle would rise to the normal operating range during warm up, then rapidly move down to the cold range. A conclusion was made that this particular malfunction was due to a defective thermostat that would stick in the full open position after reaching normal operating temperatures (around 190 degrees Fahrenheit). The material cost of the repair was $5 for a new thermostat and $8 for a gallon of new pre-mixed coolant. The customer had previously been quoted a sizable repair estimate involving having the cooling system flushed including the installation of a new heater core with new hoses.

If the thermostat replacement has not resolved an over cooling or heating problem, then replacement of the Water Temperature Sensor may be in order. This sensor works in conjunction with your car's ECU (Electronic Control Unit) to adjust the air/fuel mixture based on the coolant temperature. If the sensor is not sending the correct electrical signal, the ECU will misinterpret the signal by either over enriching or leaning the air/fuel mixture. However, over enriching of the air/fuel mixture is the usual malfunction when this sensor fails resulting in engine stalls at traffic stops. And an engine will run cooler with an enriched air/fuel mixture. The sensor is located on the bottom of the radiator opposite the coolant drain port.

1. Ensure the engine is cool and if so relieve any residual pressure in the cooling system by removing the radiator cap. Remove the lower radiator hose from the Thermostat Housing. This step may not be necessary if you feel you can remove the Thermostat Housing from the Water Pump by bending the hose.

2. Apply penetrating oil on the threads of the Thermostat Housing bolt threads.

3. Use a 10mm socket attached to a extension to remove the top nut from the Housing Stud and no extension for the lower nut. A 10mm box wrench can be used on the top nut but provide very little twisting room for the lower nut unless the oil filter is removed.

4. Remove the Thermostat Housing with a strong tug or pulling motion. Approximately 1/2 gallon of coolant will leak out when the housing is removed. The Thermostat will more than likely be stuck in the inner housing.

5. Remove the old thermostat with the attached rubber O ring. Transfer the O ring to the new thermostat or use a new O ring if necessary or desired.

6. Reverse the above steps for installation, refill the radiator with new fluid, start engine until warmed up and recheck fluid levels after cool down. Allowing the engine to idle for 1/2 hour with the radiator cap off can help remove air pockets.

The easiest method of getting to and replacing theTemperature Sensor is by removing the passenger side fan shroud assembly.

1. Disconnect the fan motor electrical connector.

2. Remove the 2 10mm shroud bolts that secure the shroud to the radiator.

3. Lift out the shroud from the lower radiator shroud sockets.

4. The Temperature Sensor is now exposed. Detach the electrical connector. Use a open end or box wrench to spin off the sensor. When the sensor is removed, coolant will leak out. If complete drainage is to be avoided, quickly hand screw in the new sensor while the coolant is draining out.  Lastly, there is an O ring attached to the sensor so ask for it when purchasing a new sensor.

5. Reverse the above steps for re-assembly and replenish the leaked out coolant.