Yamaha - Thermostat Seal Cooling System 6E5-12412-00-00. Overview. This is one of those small seals that can cause bigger cooling issues if it's not doing its job right. Around the thermostat, everything depends on a tight seal to keep water flowing where it should. I've seen engines run hotter than they should just because this seal was worn or flattened out. It's a simple replacement, but it helps keep the cooling system working the way Yamaha designed it.. Key Features. Secure Thermostat Sealing - Creates a tight seal to keep water flowing properly through the cooling system.. Heat-Resistant Material - Built to handle constant temperature changes without breaking down.. Prevents Cooling Leaks - Helps maintain proper pressure and eliminates unwanted water loss.. OEM Fit Design - Matches original specifications for proper placement and easy installation.. Engine & Boat Compatibility. Designed for Yamaha 2-stroke outboard engines with standard thermostat-controlled cooling systems. Com