Thermostat with housing suitable for BMW. A combustion engine must operate within a certain temperature window in order to function optimally. The temperature is controlled by a coolant and a thermostat. The thermostat ensures that the engine reaches its ideal operating temperature as quickly as possible and then maintains it continuously. A defective or blocked thermostat can cause the engine to overheat. This is why febi only offers coolant thermostats in OE matching quality.