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With the water pump and radiator removed from the truck, cooling-system diagnostics continue in an effort to identify any existing problems before making a trip to the auto center to purchase replacement parts. The process continues with a check of the thermostat and engine-temperature sensor.
- The thermostat is located inside the thermostat housing on the front of the engine. The thermostat will need to be removed from the engine and checked.
- In addition, the coolant-temperature sensor will be checked. This sensor tells the temperature gauge on the dash how hot the engine is running.
- Thermostats are fairly simple mechanical devices that use a spring-loaded diaphragm to allow or restrict coolant flow to the radiator. They can fail in a number of ways.
- Because thermostats are so inexpensive (around $10), it's advisable to go ahead and replace the thermostat whenever doing moderate to major cooling-system repairs.
- Some thermostats are marked indicating which direction they should be installed. If yours is not marked, check your repair manual for the proper orientation.
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In the event of an engine overheating (which has happened several times previously on our project vehicle), the temp sensor can be damaged by the excessive heat. For that reason, it's a good idea to check them and, if necessary, replace them.
- On our vehicle, the temp sensor is a one-wire sensor, meaning that the sensor itself is screwed into the intake manifold which provides an electrical ground.
- The temp sensor a variable-resistance sensor. To check the coolant-temperature sensor yourself, a DVOM or digital volt/ohm meter is used to check the resistance of the meter to verify that it is working.
- With the ohm scale on the meter set to 20k, the black lead is connected to ground and the red is brought into contact with the terminal on the sensor. On our sensor, we got a resistance reading of .40. Generally, any resistance at all indicates a working sensor, so ours checked out OK.
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