Chrysler Full-Size Trucks 1967-1988 Repair Guide

Sending Units and Sensors

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Before proceeding with sensor removal you will need to purchase a new sensor and possibly a gasket or O-ring whichever is needed for your truck.

REMOVAL & INSTALLATION

Oil Pressure Sensor

See Figure 1

The oil pressure sending unit and oil pressure gauges are warning switches and need to be taken seriously if the light is on or gauge is low. This could mean the death of your engine if ignored for long enough; an expensive mistake.

These sensors are mounted on the engine and are controlled by the oil pressure. When the pressure is high, the switch is held in the off or open position allowing no current to flow to the oil pressure warning lamp on the instrument panel. When the oil pressure switch is in the low, on or open position, current is permitted to flow to the oil pressure switch warning lamp. This will cause the light to illuminate telling you that oil is needed immediately. You should always keep a quart of oil in your vehicle at all times in case of such an emergency.



Click image to see an enlarged view

Fig. Fig. 1: 3-Prong Oil Pressure Switch

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the terminal ends on the unit.
  4.  
  5. Spray lubricant on the unit, to ensure an easy removal.
  6.  
  7. With a suitable open-end wrench or a socket, unscrew the sending unit.
  8.  

To install:
  1. Make sure area is clean before replacing the sensor. Scrape any remaining gasket material that may be left behind. Use a wire brush or a gasket scraper.
  2.  
  3. Lube the threads with oil on the new sensor 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.
  4.  
  5. Connect the wires on the sensor.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Start engine and look for any leaks in case the sensor is not tight enough.
  10.  

Coolant Sensor

The coolant 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 at its normal location between cold and hot. 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.

If the engine has been run recently, allow time to cool down before servicing.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system into a suitable container. Just enough coolant should be removed to drop the system to a level below the sensor.
  4.  
  5. Spray lubricant on the unit, to ensure an easy removal.
  6.  
  7. Disconnect the coolant sensor wires from the unit.
  8.  
  9. Unscrew the sending unit, using a suitable open-end wrench or a socket.
  10.  

To install:
  1. 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
  2.  
  3. Lube the threads with clean coolant on the new sensor 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.
  4.  
  5. Connect the wires on the sensor.
  6.  
  7. Fill the cooling system with coolant.
  8.  
  9. Connect the negative battery cable.
  10.  
  11. Start the vehicle, and check for leaks. Also check the temperature gauge.
  12.  
  13. When the job is complete, make sure the vehicle has enough coolant in the radiator or expansion tank, if equipped.
  14.  

 
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