Yamaha - Thermostat Cover Cooling System Housing YF1-55317-32-61. Overview. When you're servicing a Yamaha cooling system, the thermostat cover is one of those parts that keeps everything sealed and flowing the way it should. The Yamaha Thermostat Cover YF1-55317-32-61 secures the thermostat in place and helps contain the cooling system so water can circulate properly through the engine. It might look simple, but it plays a key role in maintaining proper engine temperature. When the cooling syst