Yamaha Thermostat 6FM-12411-00-00. Overview. The Yamaha 6FM-12411-00-00 Thermostat is a genuine original equipment manufacturer component designed to regulate engine temperature by controlling the flow of coolant within the cooling system. The thermostat automatically opens and closes based on engine temperature, allowing coolant to circulate when necessary to maintain optimal operating conditions.. Maintaining the correct engine temperature is essential for efficiency, performance, and long ter