Yamaha - Thermostat Assembly Engine Cooling System YF1-55317-30-13. Overview. Thermostats are one of those parts that quietly keep everything in check until they don't. I've worked on plenty of Yamahas where overheating or inconsistent temps traced back to a sticking thermostat. The Yamaha Thermostat Assembly YF1-55317-30-13 helps keep coolant flowing at the right time so the engine runs steady, not too hot and not too cold. It's a simple swap that can save you from bigger cooling issues down the road.. Key Features. • Precise Temperature Regulation - Controls coolant flow to maintain proper engine operating temperature.. • Yamaha Engineered Fit - Built to factory specs for accurate performance and proper sealing.. • Consistent Valve Operation - Opens and closes reliably with temperature changes for stable cooling.. • Heat-Resistant Construction - Designed to handle repeated thermal cycles in marine conditions.. • Direct Replacement Assembly - Installs easily during routine cooling sys