300 V6-3.5L (2008)
Thermostat: Testing and Inspection
ENGINE COOLANT THERMOSTAT
The thermostat is operated by a wax filled chamber (pellet) which is sealed. When heated coolant reaches a predetermined temperature the wax pellet
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.
Thermostat diagnostics is included in powertrain control module's (PCM) programing for on-board diagnosis. The malfunction indicator light (MIL) will
illuminate and a diagnostic trouble code (DTC) will be set when an "open too soon" condition occurs. Do not change a thermostat for lack of heater
performance or temperature gauge position, unless a DTC is present. For other probable causes, See: Testing and Inspection/Cooling System - Diagnosis
and Testing. Thermostat failing shut is the normal long term mode of failure, and normally, only on high mileage vehicles. The temperature gauge will
indicate this See: Testing and Inspection/Cooling System - Diagnosis and Testing.
