A thermostat is like a valve that opens and closes to keep the coolant inside the engine or to let it out. It is mounted inside the thermostat housing.
It opens mechanically when the coolant reaches a certain temperature (about 195 F on most cars).
When you start your car in the morning, your engine is cold and the thermostat is closed.
The coolant is trapped inside the engine and can't go back to the radiator. As the engine warms up, the coolant warms up. Once the engine and the coolant are warm, the thermostat opens and the coolant leaves the engine to go back to the radiator thru the top hose. The coolant goes thru the radiator where it cools down and is then pumped back into the engine thanks to the water pump. At this point, the purpose is to cool down the engine; but when the engine is cold, the thermostat is closed so that your engine warms up quickly and goes quickly into close loop.
Without a thermostat, your coolant would go thru the engine and go right back to the radiator. Your car would be overcooling, and it would take forever for your car to warm up; which brings us to one of the symptom:
If your car takes an unusually long time to warm up, chances are your thermostat is stuck open (meaning it failed and it doesn't close anymore, resulting in coolant exiting the engine even when the engine is cold).
If your car starts overheating, you could have a thermostat stuck closed (meaning it failed and it doesn't open anymore, resulting in coolant not exiting the engine and becoming unable to absorb the heat from the engine).
In both case you need a new thermostat.
Thursday, October 16th, 2008 AT 3:52 PM