Yamaha Radiator Cap Assembly YF1-72147-20-20. Overview. The Yamaha YF1-72147-20-20 Radiator Cap Assembly is a genuine original equipment manufacturer component designed to seal the radiator and maintain proper pressure within the cooling system. This cap helps regulate coolant pressure, allowing the cooling system to operate efficiently while preventing coolant loss and protecting internal engine components.. Maintaining the correct pressure within the cooling system is essential for effective h