Mishimoto has developed a racing thermostat engineered specifically for the 1999-2006 BMW E46 323i / 325i / 328i / 330i. The Mishimoto BMW Racing Thermostat fits all M52 / M54 / M56 engines. It will promote greater cooling efficiency throughout your engine. Mishimoto racing thermostats will significantly lower high engine temperature produced by modified and upgraded M52 / M54 / M56 engines. Once the engine is fully warmed up the Mishimoto Racing Thermostat will open up at a lower temperature than the stock thermostat, allowing the coolant to flow through the engine sooner thus reducing and maintaining cooler engine temperatures. And improving long term reliability of your vehicle's cooling components.