Yamaha - Thermostat Cooling System Temperature Control 6F5-12411-03-00. Overview. The Yamaha Thermostat 6F5-12411-03-00 is one of those parts that keeps your engine running at the right temperature without you thinking about it. When it starts sticking or wearing out, you'll notice it with overheating, running too cool, or inconsistent performance. It controls when water flows through the engine, so everything depends on it opening at the right time. If your motor isn't holding a steady temp, this is one of the first things to check.. Key Features. • Accurate Temperature Control - Regulates water flow to maintain proper engine operating temperature.. • OEM Fit Precision - Built to Yamaha specifications for correct function and proper sealing.. • Supports Engine Efficiency - Helps maintain optimal combustion and consistent performance.. • Heat-Resistant Construction - Designed to handle continuous temperature cycles and marine use.. Engine & Boat Compatibility. • 9.9 Present• 15 Present