GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Coolant Temperature Sender/Switch



This switch activates a warning lamp in the instrument cluster if the engine overheats. With optional instrumentation, a temperature gauge replaces the warning lamp and the temperature switch is replaced with a sending unit. It does this by changing resistance as coolant temperature increases or decreases.

The engine coolant temperature switch will close the circuit to the temperature indicator, when the coolant reaches the temperature range indicated on the sending switch. The engine coolant temperature switch is not serviceable. If it is malfunctioning, it should be replaced.

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Typical temperature sending switches.


  1. Remove the temperature sender from the engine.
  3. 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.
  5. 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.
    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.

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