Yamaha - Thermostat Cover Cooling System Housing 6AH-12413-00-1S. Overview. This is one of those parts that quietly keeps your cooling system sealed and working right. The thermostat cover holds everything in place and keeps water flowing where it needs to, without leaks or pressure loss. When it's in good shape, you don't think about it-but once it warps or corrodes, cooling issues can start showing up fast. It's a simple piece, but it plays a big role in keeping your engine running at the right temperature.. Key Features. Secure Thermostat Housing - Keeps the thermostat properly enclosed for consistent cooling operation.. Leak-Resistant Fit - Designed to seal tightly and prevent water loss or pressure issues.. OEM Fit and Alignment - Matches Yamaha specifications for proper installation and function.. Marine-Ready Construction - Built to handle heat cycles and exposure to water environments.. Engine & Boat Compatibility. Designed for Yamaha outboard engines using this style of thermo