Thermostat
Thermostat TestA new thermostat should be installed only after the following tests have been carried out.
Thermostat Test, Electrical
WARNING: Always vent the exhaust to the outside when carrying out this test. Failure to follow this instruction can result in personal injury.
NOTE: On vehicles with 98°C (208°F) electronic thermostats, the thermostat must be removed to access the terminals. Once the thermostat has been removed, check the resistance between the terminals. The resistance should measure 15 ohms ± 2 ohms or a new thermostat must be installed.
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 engine OFF, disconnect the cylinder head temperature (CHT) sensor electrical connector and attach the service coolant temperature monitor harness as a jumper between the PCM and the CHT. Attach a 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 harness. A scan tool can also be used to monitor the CHT on vehicles equipped with a data link connector (DLC).
Thermostat Test, Mechanical
NOTE: Fully open means the thermostat valve lifts a distance of 5.8 mm (0.22 inch) or more off the valve seat.
Remove the thermostat and immerse in a hot antifreeze and water mixture. The thermostat will open when the mixture has reached the standard operating (STO) temperature ± 2°. The STO temperature is marked on the thermostat. Install a new thermostat if it does not operate as specified.
The following STO temperature thermostats are available:
^ 82°C (180°F)
^ 90°C (194°F) or
^ 98°C (208°F)
If heat is not available, check the thermostat for leakage. Hold the thermostat up to a lighted background. Leakage of light around a new 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. This is considered normal.