Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Coolant Temperature Sensor

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OPERATION



See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Cutaway view of 1.2L, 1.6L, 1.8L and 2.7L engines' thermometer



Click image to see an enlarged view

Fig. Fig. 2: Cutaway view of 2.2L, 2.5L and 3.3L engines' thermometer

The coolant temperature sensor, or Thermometer as it is referred to by Subaru, is installed in either the intake manifold (1.2L engines), the side of the radiator( 1.6L, 1.8L and 2.7L), or separate water pipe connecting the cylinder heads (2.2L, 2.5L and 3.3L engine), and monitors the coolant temperature. A signal is sent from the sender to the engine temperature gauge in the combination meter, and also to the ECU where the radiator fan operation signal is generated. In addition to fan operation, the ECM uses coolant temperature to adjust fuel delivery and ignition timing.

TESTING



See Figure 3

Click image to see an enlarged view

Fig. Fig. 3: Schematic of thermometer and gauge

  1. Refer to the illustration and connect the temperature gauge and sender in series.
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  3. Make sure that the gauge indicates C when the ignition switch is OFF .
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  5. Start the vehicle and record the resistance with a multimeter or equivalent at the sender.
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  7. At 122°F (50°C) the correct resistance should be between 133.9-178.9 ohms. At 176°F (80°C) the correct resistance should be between 47.5-56.8 ohms. At 212°F (100°C) the correct resistance should be between 26.2-29.3 ohms. And at 248°F (120°C) the correct resistance should be between 14.9-17.3 ohms.
  8.  

REMOVAL & INSTALLATION




CAUTION
Use extreme care if removing a sender from a vehicle which has been driven recently. The coolant could be extremely hot.

  1. Disconnect the negative battery cable.
  2.  
  3. Access the thermometer on the intake manifold (1.2L engine), radiator (1.6L, 1.8L, 2.7L engines), or coolant pipe (2.2L, 2.5L and 3.3L engines) and unfasten the wire harness attached.
  4.  
  5. Loosen the draincock at the lower portion of the radiator and drain enough coolant into a suitable container to bring the level below the thermometer.
  6.  
  7. Loosen and remove the thermometer. Inspect the threads of the manifold, radiator or pipe, and use a thread chaser to restore the threads if damaged.
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  9. If reinstalling the original thermometer, remove sealing gasket and replace with a new one.
  10.  

To install:
  1. Position thermometer, and new sealing gasket into hole in manifold, radiator or coolant pipe, depending on model, and hand-tighten.
  2.  
  3. Using an appropriate socket, tighten the thermometer to 2-3 ft. lbs. (3-4 Nm).
  4.  
  5. Connect the wire harness to the thermometer. Tighten the radiator draincock, if not already done.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Fill the cooling system with coolant and bleed.
  10.  

 
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