97 - 01 Toyota Camry Thermostat and Temperature Sensor Replacement
I. Replacing the Thermostat
On rare occasions, in high-mileage Camrys, the cooling system's thermostat may fail. A thermostat may lock up in either the open or closed position resulting in overcooling or overheating.
In one case when a thermostat failed, the customer complained that he was getting heat in the cabin. He said the temperature gauge on the dashboard would rise to the normal operating range during warmup, then rapidly move down to the cold range. I concluded this particular malfunction was due to a defective thermostat that would stick in the fully open position after reaching normal operating temperatures (around 190 degrees Fahrenheit). The only material cost of repairing this problem 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 flushing the cooling system and installing a new heater core with new hoses.
Thermostat Replacement Procedure
1. First, make sure the engine is cool. Then 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.
3. Use a 10 mm socket attached to a extension to remove the top nut from the housing stud. Use no extension for the lower nut. A 10 mm box wrench can be used on the top nut, but there is very little twisting room for the lower nut unless the oil filter is removed.
4. Remove the thermostat housing with a strong tugging or pulling motion. Approximately 1/2 gallon of coolant will leak out when the housing is removed. The thermostat will most likely be stuck inside the 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 you want.
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.
2. Replacing the Temperature Sensor
If the car continues to overheat even after installing a new thermostat, the problem could be caused by either a defective temperature sensor or a defective fan motor. Replacement of the water temperature sensor may be in order. This sensor is located on the bottom of the radiator opposite the coolant drain port. It 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 making the air/fuel mixture too rich or too lean. Most commonly, a malfunction of this sensor results in over-enriching the air/fuel mixture, causing the engine to stall at traffic stops. And an engine will run cooler with an enriched air/fuel mixture.
Temperature Sensor Replacement Procedure
This sensor has an O-ring, so ask for the O-ring when you buy a new sensor.
The easiest method of getting to and replacing the temperature sensor is by removing the passenger-side fan shroud assembly.
1. Disconnect the fan motor electrical connector.
2. Remove the two 10 mm shroud bolts that secure the shroud to the radiator.
3. Lift out the shroud from the lower radiator shroud sockets. The fan motor can be tested by applying 12 volts to the motor connector leads.
4. The temperature sensor is now exposed. Detach the electrical connector.
5. Use an open-end or box wrench to spin off the sensor. Once the sensor is removed, coolant will start leaking out. To keep all the coolant from draining out, quickly screw in the new sensor by hand. Don't forget the O-ring attached to the sensor.
6. Reverse the above steps for re-assembly, and replenish the leaked-out coolant. I recommend using only genuine Toyota coolant.