Thermostat: Testing and Inspection
ThermostatA new thermostat should be installed only after the following electrical and mechanical tests have been carried out.
Thermostat Electrical Test
NOTE: The electrical thermostat test is most accurate if carried out indoors at less than 37.8°C (100°F) ambient air. This test may be carried out with or without the hood open and with the engine warm or cold.
1. Check the engine coolant level. Fill as needed.
2. With the ignition OFF, voltage values (0 5 V) may now be monitored while the sensor retains its connection to the wiring harness.
A diagnostic tool may be used to monitor the ECT on vehicles equipped with Data Link Connector (DLC).
3. Place the transmission in PARK (P) or NEUTRAL (N).
4. Start the engine and allow the engine to idle throughout this test. Allow the engine to run for 2 minutes, then record the ECT voltage. Record the ECT voltage every 60 seconds. When the ECT voltage trend changes direction or only changes slightly (0.03 volt or less) from the previous reading, record this as the thermostat opening voltage. Use the voltage and corresponding coolant temperature chart listed below.
5. If the thermostat opening voltage is greater than 0.58 volt and less than 90°C (194°F), install a new water thermostat.
6. If the thermostat opening voltage is less than 0.58 volt and greater than 90°C (194°F), the thermostat is good and a new thermostat should not be installed. GO to Symptom Chart for further instructions.
Thermostat Mechanical Test
1. Remove the thermostat.
2. Check the thermostat for seating. Hold the thermostat up to a lighted background. Leakage of light around the thermostat valve at room temperature indicates that a new thermostat should be installed. Some thermostats have a small leakage notch at one location on the perimeter of the thermostat valve, which is considered normal.
3. Immerse the thermostat in a boiling antifreeze and water mixture.
4. See the General Specifications chart for thermostat opening temperatures.
Radiator Leak Test, Removed From Vehicle
CAUTION: Never leak test an aluminum radiator in the same water that copper/brass radiators are tested in. Flux and caustic cleaners may be present in the cleaning tank and they will damage aluminum radiators.
NOTE: Always install plugs in the transmission fluid cooler fittings before leak testing or cleaning any radiator.
1. Leak test the radiator in clean water with 138 kPa (20 psi) air pressure.
Fan Clutch Test
1. Spin the fan blade by hand. A light resistance should be felt, but the fan will not spin freely if spun by hand. If there is no resistance or very high resistance, the fan speed must be checked as follows:
2. A slight fan wobble is allowable by design, unless the wobble causes noticeable vibrations to the vehicle.
Fan Clutch Test Minimum Speed Requirement
WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.
1. Use a suitable marker to mark the coolant pump pulley and one of the fan blade retaining bolts.
2. Connect a tachometer to the engine.
3. Install the diagnostic tool.
4. Connect a digital photoelectric tachometer.
5. Start the engine and run it at approximately 1,500 rpm (for at least 2 minutes) until the normal operating temperature has been achieved. The A/C must be OFF.
6. Operate the digital photoelectric tachometer at 3,000 rpm and aim it at the coolant pump pulley. Using the diagnostic tool, adjust the engine speed until the light flash and the coolant pump pulley mark are synchronized.
7. Aim the digital photoelectric tachometer at the fan blade bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
8. The fan blade speed must not be greater than 1,500 rpm at 3,000 coolant pump rpm.
9. Turn the engine OFF.
10. NOTE: A new fan blade must not be installed unless physical damage is observed. An undamaged blade can be reused with a new fan clutch.
If the fan blade speed was greater than 1,500 rpm, install a new fan clutch.