Yamaha - Thermostat - 69M-12411-01-00Yamaha Thermostat Engine Cooling Control Component 69M 12411 01 00 Overview A motor that runs too cold or too hot is going to give you problems sooner or later. The thermostat is what keeps everything in that sweet spot so the engine warms up properly and stays there. When its working right, you get smooth performance and better efficiency without even thinking about it. But when it sticks or fails, youll see it fast with temperature issues or