Chrysler Front Wheel Drive Cars 6-CYL 1988-1995 Repair Information

Coolant Temperature Sensor

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OPERATION



See Figures 1 and 2

The engine coolant temperature sending unit, not to be confused with the engine temperature sensor which is used for the fuel injection system, is a variable resistor. The sending unit decreases its circuit's resistance as the temperature of the engine coolant rises.

There are two types of engine coolant temperature sending units in the vehicles covered by this information. The Premier and Monaco have dual-circuit sending unit. It consists of one circuit for a warning lamp and another circuit for the temperature gauge in the instrument panel.



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Fig. Fig. 1: Engine coolant temperature sending unit and other sending unit locations-3.0L engines except Premier and Monaco



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Fig. Fig. 2: Engine temperature sending unit-3.3L and 3.8L engines

The temperature sending unit for all other models only contains one circuit for the temperature gauge. This circuit has a variable resistor. The wire for this sending unit is yellow with a tracer, and the sending unit is located on the right side of the engine.

TESTING



Premier and Monaco

See Figure 3

When testing the engine coolant temperature sending unit, you are actually testing two independent circuits. The first circuit (right-hand terminal with the locking tang up) is the circuit for the engine temperature warning/indicator light. The circuit is normally an open circuit until the engine reaches a dangerously high temperature. When the temperature becomes this elevated, a switch closes in the sending unit, thereby grounding and completing the circuit for the light bulb in the lamp. The indicator lamp in the dashboard illuminates. This light should, however, only illuminate when the engine has reached a high temperature and the sending unit is working.



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Fig. Fig. 3: Engine temperature sending unit schematic-Premier and Monaco models

The second circuit is that of the temperature gauge in the instrument cluster. The sending unit left-hand terminal is connected to a variable resistor in the sending unit itself. The resistance of the entire circuit is changed depending on the temperature of the engine coolant. The temperature gauge reads the changes in resistance and converts them into the movement of the gauge needle. The resistance of this circuit should never be infinite (open circuit) and should change smoothly and evenly when heated or cooled.

Perform this test on a cold or cool engine.

  1. Disconnect the negative (-) battery cable.
  2.  
  3. Unplug the electrical wiring from the sending unit.
  4.  
  5. Using an ohmmeter, measure the resistance between the right terminal (with the locking tang of the sending unit facing upward) and the sending unit's metal body.
    1. Infinite resistance (open circuit): continue to the next test.
    2.  
    3. Anything but infinite resistance (grounded circuit): the sending unit is bad, replace with a new one.
    4.  

  6.  
  7. Measure the resistance between the left terminal (with the locking tang of the sending unit facing upward) and the sending unit's metal body:
    1. Infinite resistance or zero resistance: the sending unit is bad, replace the sender with a new one.
    2.  
    3. Other than infinite or zero resistance: continue to the next step.
    4.  

  8.  
  9. Remove the temperature sender from the center front of the engine (Premier and Monaco) or from the water box on the engine (except Premier and Monaco).
  10.  
  11. Position the water temperature sending unit in such a way that the metal shaft (opposite end from the electrical connectors) is situated in a pot of water. Make sure that the electrical connectors are not submerged and that only the tip of the sending unit's body is in the water.
  12.  
  13. Heat the pot of water at a medium rate. While the water is warming, continue to measure the resistance of the left terminal and the metal body of the sending unit:
    1. As the water warms up, the resistance exhibited by the ohmmeter goes down in a steady manner: the sending unit is good.
    2.  
    3. As the water warms up, the resistance does not change or changes in erratic jumps: the sender is bad, replace it with a new one.
    4.  

  14.  
  15. Install the good or new sending unit into the engine, then connect the negative battery cable.
  16.  

Except Premier and Monaco

See Figure 4

This circuit is that of the temperature gauge in the instrument cluster. The sending unit terminal is connected to a variable resistor in the sending unit itself. The resistance of the entire circuit is changed depending on the temperature of the engine coolant. The temperature gauge reads the changes in resistance and converts them into the movement of the gauge needle. The resistance of this circuit should never be infinite (open circuit) and should change smoothly and evenly when heated or cooled.



Click image to see an enlarged view

Fig. Fig. 4: Coolant temperature sending unit schematic-except Premier and Monaco models

Perform this test on a cold or cool engine.

  1. Disconnect the negative (-) battery cable.
  2.  
  3. Unplug the electrical wiring from the sending unit.
  4.  
  5. Using an ohmmeter, measure the resistance between the terminal and the sending unit's metal body
    1. Infinite resistance or zero resistance: the sending unit is bad, replace the sender with a new one.
    2.  
    3. Other than infinite or zero resistance: continue to the next step.
    4.  

  6.  
  7. Remove the temperature sender from the engine.
  8.  
  9. Position the water temperature sending unit in such a way that the metal shaft (opposite end from the electrical connectors) is situated in a pot of water. Make sure that the electrical connector is not submerged and that only the tip of the sending unit's body is in the water.
  10.  
  11. Heat the pot of water at a medium rate. While the water is warming, continue to measure the resistance of the terminal and the metal body of the sending unit:
    1. As the water warms up, the resistance exhibited by the ohmmeter goes down in a steady manner: the sending unit is good.
    2.  
    3. As the water warms up, the resistance does not change or changes in erratic jumps: the sender is bad, replace it with a new one.
    4.  

  12.  
  13. Install the good or new sending unit into the engine, then connect the negative battery cable.
  14.  

REMOVAL & INSTALLATION



See Figures 1 and 2


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system until the coolant level is below the coolant sensor.
  4.  
  5. Detach the electrical connector from the sensor.
  6.  
  7. Remove the sensor from the engine. On some applications, the coolant sensor threads into the thermostat housing.
  8.  
  9. Installation is the reverse of the removal procedure. Fill and bleed the cooling system.
  10.  

 
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