How to Replace a Coolant Temperature Sensor

  • 1-2 hours
  • Beginner
  • 15-35
What You'll Need
Catch pan
Set of metric wrenches
Open end box end wrench
Teflon tape
1 gallon of antifreeze
Mechanics gloves
Socket and ratchet set (optional)
Fender cover
Safety glasses

A coolant temperature sensor gauges the temperature of a vehicle’s engine. Positioned close to the thermostat, it forwards temperature messages to the automobile’s control computer, which can be seen by the driver on the temperature gauge in the dashboard. The temperature readings taken by the coolant temperature sensor is important, as this information is responsible for adjustments to the vehicle's fuel mixture, which is necessary for optimal functioning of the engine and for operating the engine’s cooling fans.

Coolant temperature sensors are prone to corroding over time. Certain makes of automobile do not have an engine temperature gauge on the dashboard, and in these vehicles, the engine temperature is indicated by a warning light once it becomes too high. A corroded coolant temperature sensor will give an incorrect reading. It is, therefore, important to replace the coolant temperature sensor as soon as it shows signs of corrosion.

Step 1: Partly Drain the Radiator

Allow the engine to cool so that you do not get burned. Place a catch pan under the radiator once you can touch the engine. Drain approximately 1 gallon of antifreeze from the radiator. Unplug the electrical connections on the coolant temperature sensor.

Step 2: Disconnect and Remove the Sensor

You will find the coolant temperature sensor screwed into the engine (usually on driver side). The coolant temperature sensor has a wire lead running from it. Disconnect this wire and insure that the insulation is neither melted nor discolored. You will need to replace the wire if either condition exists.

Use the open end box end wrench to loosen the temperature sensor initially by turning in a counter clockwise fashion. Thereafter, use your hand to loosen the sensor completely. Remove the corroded coolant temperature sensor from the engine. Wind Teflon tape around the threads of the replacement coolant temperature sensor.

Step 3: Plug Wiring into Sensor

Position the coolant temperature sensor in the engine block. Tighten gently, as over tightening will damage the sensor and cause it to give faulty readings. Plug the electrical wiring into the replacement sensor.

Step 4: Fill Radiator

Replace the antifreeze that you previously drained out. With the radiator cap off, turn the engine and heater on and allow it to warm up. Once the temperature in the radiator reaches 195 degrees F, the thermostat will kick in, and as trapped air is expelled, the antifreeze will begin to circulate. Fill the radiator and replace its cap.

Step 5: Test Sensors

Check that the fans begin to operate once engine temperature has reached 215 degrees F. If the fans are functioning correctly, you have successfully replaced the sensors.

Step 6: Test Coolant Flow

Because you have removed an amount of antifreeze, you must check that the coolant is flowing correctly after replacing the coolant temperature sensor. To do this, squeeze the hose (wear gloves) to gauge if there is any pressure. If there is pressure, the coolant is flowing.