Yamaha - Thermostat Cooling System Component 6AH-12411-00-00. Overview. On smaller Yamaha motors like the F15 and F20, keeping the engine at the right temperature makes a bigger difference than most people think. I've seen engines run rough or inefficient just because the thermostat wasn't doing its job. When it's working right, the motor warms up properly and stays consistent no matter how long you're running. It's one of those simple parts that keeps everything running smooth and efficient.. Key Features. • Temperature Regulation Control - Opens and closes at set temperatures to maintain proper engine heat levels.• Consistent Engine Warm-Up - Helps the engine reach optimal operating temperature quickly and stay there.• Improved Combustion Efficiency - Supports better fuel burn by maintaining stable temperature conditions.• Engine Protection Support - Helps prevent overheating and reduces internal wear over time.• Factory-Spec Fitment - Designed to match Yamaha cooling systems for pro