Mazda 323/MX-3/626/MX-6/Millenia/Protégé 1990-1998 and Ford Probe 1993-1997

Water Thermosensor (Coolant Temperature Sensor)

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OPERATION



The coolant temperature sensor is a variable resistor that is influenced by temperature. Which means, as the temperature changes, so does the resistance inside the sensor. The computer reads this change in resistance to determine the operating temperature of the engine. It uses this reading to determine proper air/fuel mixture and ignition timing settings.

TESTING



See Figures 1 and 2

This test can also be performed with the sensor still installed in the motor, provided the engine is at the same temperatures as given for the specifications.



Click image to see an enlarged view

Fig. Fig. 1: To test the sensor while still installed in the engine, verify the temperature of the sensor then take the resistance reading



Click image to see an enlarged view

Fig. Fig. 2: The end of the temperature sensor can be submerged in cold or hot water to check the resistance

  1. Remove the thermosensor.
  2.  
  3. Place the sensor in water with a thermometer and heat the water gradually.
  4.  
  5. Measure the resistance of the sensor and compare to the following values:

    -4°F (-20°C)-14.6-17.8 kohms
     
    68°F (20°C)-2.2-2.7 kohms
     
    104°F (40°C)-1.0-1.3 kohms
     
    140°F (60°C)-0.50-0.65 kohms
     
    176°F (80°C)-0.29-0.2 kohms
     

  6.  

REMOVAL & INSTALLATION



  1. Drain the engine coolant.
  2.  
  3. Remove the thermosensor from the rear of the engine or intake manifold.
  4.  

To install:
  1. Install a new sealing washer to the thermosensor.
  2.  
  3. Torque the sensor to 18-22 ft. lbs. (25-29 Nm).
  4.  

 
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