The combustion of air and fuel inside an internal-combustion engine creates great amounts of heat. Without regulation, this heat can cause severe engine damage. The engine's cooling system, consisting of radiator, coolant, hoses, water pump and thermostat, regulates the engine's temperature and actually turns it into useful cabin heat. The thermostat is the gatekeeper in the process, regulating the flow of the coolant in the engine.
Thermostat's Function
The thermostat is at the connection point between the upper or lower radiator hose and the engine. The thermostat has a circular valve in the center of it that opens and closes as the coolant temperature rises and falls. The thermostat's valve remains closed until the coolant reaches the engine's correct operating temperature. When the valve opens -- at the prescribed operating temperature -- it allows the coolant to flow from the engine into the radiator for cooling. The thermostat continues opening and closing as you drive, to maintain the engine's optimal operating temperature.
Thermostat Stuck Closed
When the thermostat on your vehicle sticks in the closed position, coolant cannot flow from the engine to the radiator. This forces the coolant to remain in the engine and warm up along with the engine. This results in engine overheating -- a condition that can result in complete engine failure. When the thermostat sticks closed, you must replace it to repair the problem.
Thermostat Stuck Open
The valve in the center of the thermostat can also stick open. This allows the coolant to flow between the engine and radiator without restriction, which results in over-cooling. Over-cooling causes poor fuel economy and an incorrectly operating heating system -- cool air coming from the vents when the heater is on. When the thermostat sticks open, replacing the thermostat is the only way to repair the problem.
Delayed Thermostat Response
The thermostat can sometimes open and close at a delayed rate. This is typically caused by corrosion, sludge build-up, thermostat spring failure or even the thermostat being installed backwards. When this occurs, the vehicle's coolant temperature will rise to higher than normal, but never reach the "Hot"l range on the temperature gauge. In this case, you can attempt to flush sludge from the cooling system to see if that eliminates the symptom.
