In contrast to the thermostat in your house, the thermostat in your BMW can’t precisely regulate the temperature of your car engine. What it does do is allow your vehicle to quickly warm to a certain point, then allow the full cooling system to regulate things after that point. To do that, the BMW Thermostat stays closed while the car is cold, shutting the engine off from the radiator. It doesn’t take long to heat things up with no water circulation, and when the water is warm enough the thermostat opens and allows water to flow to the radiator.

Most of the time, the BMW thermostat is of the pellet-type, and it’s opening is regulated by a pellet of wax. The wax has a very specific melting point—usually 165 degrees, 185 degrees, or 195 degrees—and when it melts, the thermostat opens. The temperature at which your BMW thermostat opens can have a big effect on your car’s emissions, so make sure you replace your BMW thermostat with an new one having the correct temperature rating.