Prowler V6-3.5L VIN G (1999)
Thermostat: Testing and Inspection
The thermostat is operated by a wax filled container (pellet) which is sealed so that when heated to a predetermined temperature, the wax expands
enough to overcome the closing spring and water pump pressure, which forces the valve to open. Coolant leakage into the pellet will cause a
thermostat to fail open. Do not attempt to free up a thermostat with a screwdriver.
The open too soon type failure mode is included in the on-board diagnosis. The check engine light will not be lit by an open too soon condition. If it
has failed open, a DTC diagnostic trouble code will be set. Do not change a thermostat for lack of heat by gauge or heater performance, unless a code
is present, see Cooling System Diagnosis for other probable causes. Failing shut is the normal long term mode of failure, and normally, only on high
mileage vehicles. The temperature gauge will indicate this.