Diagnostic Aids

NOTE: The engine coolant temperature (ECT) sensor is mounted on the engine and the radiator coolant temperature (RCT) sensor is mounted on the radiator.

As the thermostat opens, the RCT sensor temperature should rise steadily, then stabilize once the thermostat opens completely.
Test the RCT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor.
If the vehicle has sat for greater than 8 hours, the ECT sensor and the RCT sensor values should display within 3°C (5°F).