Thermostat

A component that helps regulate engine temperature by controlling the speed at which coolant circulates through the engine. The thermostat stays closed until the engine reaches a set temperature. This is usually around 180 or 190 degrees F. The higher the engine temperature the better the efficiency. But, the engine cannot get too hot or it will overheat.

It also helps the engine to warm up quicker so you can get heat from the vents.

When the thermostat opens, then engine coolant is allowed to flow into the radiator to be cooled down and then returns to the engine. The thermostat works just like the one in your home. It opens and closes (turns on and off) to keep the engine near a steady temperature.