Yamaha - Thermostat Cover Cooling System Component 6DA-12413-00-9S. Overview. If you've spent any time around Yamaha cooling systems, you know even small sealing parts matter. This thermostat cover keeps everything tight around the thermostat so water flows the way it should and the engine stays in its proper temp range. When these start to wear or corrode, it doesn't take long before you're chasing leaks or uneven temps. It's a straightforward fix that keeps your cooling system doing its job without surprises.. Key Features. Thermostat Retention - Holds the thermostat securely in place for stable temperature regulation.. Sealing Surface Integrity - Provides a clean, even surface to maintain proper gasket sealing.. OEM Fitment - Designed to match Yamaha factory specs for proper alignment and installation.. Cooling System Support - Helps ensure consistent water flow through the engine block.. Engine & Boat Compatibility. Designed for Yamaha outboards equipped with thermostat-controlled