Coolant Temperature Gauge

The coolant temperature sending unit is mounted to the engine. The unit is mounted at a point where the unit is exposed to the coolant being circulated through the engine coolant passages. The sending unit contains a temperature-sensitive variable resistor that senses and reacts to coolant temperature. Resistance decreases as temperature increases. When electric power is supplied to the engine coolant temperature gauge, current flows through the gauge. The current flows to the variable resistor and then to a ground at the engine. The position of the gauge pointer is determined by the strength of the current flowing through the gauge. When the engine coolant is cold the following situations exist:
^ The resistance is high.
^ The current flow is low.
^ The pointer indicates a cold reading.

As the coolant temperature increases, the following situations occur:
^ The resistance decreases.
^ The current flow is high.
^ The pointer moves toward the center of the gauge.

Prolonged driving or idling in very hot weather may cause the pointer to move beyond this point. An overheat condition exists if the pointer goes into the red zone at the upper limit of the scale.

Dial calibrations go far above the normal boiling point of water, which is 100°C (212°F). This is because the cooling system is pressurized. The increase in pressure also increases the boiling temperature of the coolant. This action permits the coolant to reach temperatures above those possible with a non-pressurized system without boiling. The higher operating temperature of the cooling system that results gives greater cooling efficiency and other benefits.