Coolant Temperature Sensor/Switch (For Computer): Description and Operation

Fig. 5 Coolant temperature sensor:

The coolant temperature sensor, (which is the same as engine operating temperature) Fig. 5, is mounted near the thermostat housing and provides data on engine operating temperature to the SMEC.
Incorporated in the digital microprocessor electronics are some unique spark advance schedules which will occur during cold and warm engine operation. They have been added to reduce engine emission and improve driveability. Because they will be changing at different engine operating temperatures during warm-up, all spark advance testing should be done with the engine fully warmed. This data allows the SMEC to demand slightly richer air-fuel mixtures and higher idle speeds until normal operating temperatures are reached. The sensor is a variable resistor with a range of -40 degrees F to 265 degrees F.