Yamaha - Thermostat Cover Cooling System Component 6C5-12413-00-9S. Overview. This is one of those parts that keeps the cooling system sealed and doing its job without you thinking about it. The thermostat cover holds everything in place so coolant flows the way it should through the engine. If it's cracked, warped, or not sealing right, you'll end up with leaks or temperature issues pretty quick. It's a simple piece, but it plays a big role in keeping the motor running at the right temperature.. Key Features. • Secure Thermostat Housing - Keeps the thermostat properly enclosed for consistent operation.. • Maintains System Pressure - Helps ensure proper coolant flow and temperature regulation.. • OEM Fit Accuracy - Matches Yamaha factory specs for proper sealing and alignment.. • Heat Resistant Construction - Built to handle temperature changes and marine conditions.. Engine & Boat Compatibility. Verify compatibility with your specific Yamaha outboard model and part number before insta