Coolant Temperature Sensor

The coolant temperature sensor is a variable resistor. It is located on engine block just below the No. 1 spark plug. It provides the fuel/timing control unit with information on engine temperature. When engine is below 27°F (-3°C), the sensor causes ignition timing to be advanced.

This is to ensure complete combustion of air/fuel mixture, providing good cold engine performance. Sensor also influences duty cycle during engine cranking. When temperature is less than 140°F (60°C) duty cycle (dwell) will be about 80%. At temperatures above 140°F (60°C), duty cycle will be about 50%.