Yamaha - Thermostat Gasket Cooling System Seal 6E9-12414-A1-00. Overview. I've learned the hard way not to reuse thermostat gaskets, especially on older Yamaha setups like the C40 and CV40. It might look fine at first, but once it's compressed, it doesn't seal the same twice. This gasket is what keeps the cooling system tight right around the thermostat housing. Put a fresh one in, and you avoid leaks and temperature issues before they even start.. Key Features. • Reliable Cooling System Seal - Keeps water contained within the thermostat housing for proper flow.• Leak Prevention Design - Helps eliminate coolant leaks that can affect engine performance.• Heat-Resistant Material - Built to handle engine temperature and continuous water exposure.• Precision Cut Fitment - Designed to match Yamaha surfaces for proper sealing.• Direct Yamaha Replacement - Ensures dependable installation and long-term reliability.. Engine & Boat Compatibility. Designed for Yamaha outboard engines utilizing th