Coolant Temperature Sending Unit

The coolant temperature sending unit is mounted to the engine at a point where it 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 gage, a current flows through the gage to the variable resistor and then to a ground at the engine. The position of the gage pointer is determined by the strength of the current flowing through the gage. When the engine coolant is cold, resistance is high, the current flow is low, and the pointer indicates a cold reading. As coolant temperature increases, the resistance of the sending unit resistor decreases and the pointer moves toward the center of the gage.

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 1OO°C (212°F) because the cooling system is pressurized. The increase in pressure also increases the boiling temperature of the coolant, permitting it 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.