A vehicle’s cooling system uses a thermostat valve to help regulate the engine’s temperature. When the engine is cold, the valve will be closed, bypassing the radiator and allowing the engine to rapidly come up to operating temperature. After that level has been reached, the valve on the thermostat opens to allow coolant to circulate through the radiator. But sometimes, through normal wear and tear or contaminants in the coolant, the thermostat may fail to open, causing the engine to overheat. This will be evident by the temperature gauge climbing into the high temperature (usually red) zone. Remember that a thermostat failure can also be caused by other factors, as well. For that reason, it is important to have a skilled mechanic check all the links in the chain – radiator, coolant pump, hoses and thermostat.