See Figures 1, 2, 3 and 4
The coolant temperature sensor is similar to the oil pressure switch. Except in that the temperature sending unit is controlled by the coolant not oil and it reacts to temperature not pressure. When the engine is cold the resistance of the disc in temperature sending unit is high and a low temperature will be indicated on the gauge. When your engine heats up at operating temperature the gauge will be at its normal location between cold and hot. Some gauge needle cycling for the diesel engine is normal depending on vehicle load. However, for gas or diesel vehicles, if your gauge reads HOT , or the temperature light comes on, this means there is a potential mechanical problem. Turn OFF your engine immediately. Overheating is not a pleasant thing to deal with in rush hour traffic or while on a vacation. We have all seen or at least known someone who has experienced it at one point.
When a problem occurs with a coolant temperature gauge, the sensor (sending unit) and wiring should be checked.
- Check the sending unit and wiring by grounding the connector leads at the sending unit.
- With the ignition ON , a grounded gauge will cause the coolant temperature gauge to read at or above maximum.
- If the gauge does read at or above maximum, it is still operating.
REMOVAL & INSTALLATION
If the engine has been run recently, allow it time to cool-down before servicing.
- Disconnect the negative battery cable.
- Drain the cooling system into a suitable container. Just enough coolant should be removed to drop the system to a level below the sensor.
- Spray lubricant on the unit, to ensure an easy removal.
- Disconnect the coolant sensor wires from the unit.
- Unscrew the sending unit, using a suitable open-end wrench or a deep socket.
- Make sure area is clean before replacing the sensor. Remove any gasket material that may be left behind. Use a wire brush or a gasket scraper
- Lube the threads on the new sensor with clean coolant and place the O-ring or gasket on the end going into the engine. Carefully thread the sensor by hand, making sure the threads are even, and you are not forcing the sensor into the block. Using a tool, tighten sensor but not to tight as it could break easily.
- Connect the wires on the sensor.
- Fill the cooling system with coolant.
- Connect the negative battery cable.
- Start the vehicle, and check for leaks. Also check the temperature gauge.
- When the job is complete, make sure the vehicle has enough coolant in the radiator or expansion tank, if equipped.