Thermostat

The water thermostat should be replaced only after the following tests have been carried out.

Thermostat Test, Electrical

CAUTION: Always vent the exhaust to the outside when carrying out this test.

NOTE: Procedure 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 coolant level in the radiator and engine coolant expansion tank. Fill as required.
2. With the key OFF, disconnect the Engine Coolant Temperature (ECT) sensor electrical connector and attach Service Coolant Temperature Monitor Harness as a jumper between the PCM and the ECT. Attach Digital Multimeter to the thermostat monitor harness. Voltage values (0 to 5 V) may now be monitored while the sensor retains its connection to the wiring harness.

NOTE: Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause improper diagnosis.

3. Place transmission in Park (P) or Neutral (N).





4. Start the engine and allow 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 volts or less) from the previous reading, record this as the thermostat opening voltage. Use the voltage and corresponding coolant temperature chart.
5. If the thermostat opening voltage is greater than 0.79 volts and less than 0°C (76°F), replace the water thermostat.
6. If the thermostat opening voltage is less than 0.79 volts and greater than 80°C (176°F), the water thermostat is good and should not be replaced. Refer to the Symptom Chart for further instructions.

Thermostat Test, Mechanical

NOTE: Fully open means the thermostat valve lifts a distance of 5.8 mm (0.2 inch) or more off the valve seat.

Remove the water thermostat and immerse in a boiling antifreeze and water mixture. The water thermostat should begin to open at 86 - 90°C (187 - 194°F) 2.0L engine, 84 - 88°C (183 - 190°F) 2.5L engine and be fully open at 102°C (216°F) 2.0L engine, 99°C (210°F) 2.5L engine. Install a new thermostat if it does not operate as specified.
If heat is not available, check the water thermostat for leakage. Hold the water thermostat up to a lighted background. Leakage of light around the thermostat valve at room temperature indicates that the water thermostat should be replaced. Some water thermostats have a small leakage notch at one location on the perimeter of the thermostat valve, which is considered normal.