Yamaha - Thermostat Cooling System Temperature Control 6FP-12411-00-00. Overview. The Yamaha Thermostat 6FP-12411-00-00 is one of those parts that keeps your engine running at the right temperature without you noticing it-until something's off. When it starts sticking or wearing out, you'll see it in fluctuating temps, slow warm-up, or overheating. It controls when coolant flows through the engine, so it has to open and close at the right time every time. If your motor isn't holding steady temperature, this is one of the first things worth checking.. Key Features. • Accurate Temperature Control - Regulates coolant flow to maintain proper engine operating temperature.. • OEM Fit Precision - Built to Yamaha specifications for correct operation and proper sealing.. • Supports Engine Efficiency - Helps maintain optimal combustion and consistent performance.. • Heat-Resistant Construction - Designed to handle continuous temperature cycles and marine conditions.. Engine & Boat Compatibility.