The Ford Fiesta Radiator Header Tank (Part Number 1221362) is a crucial component of the vehicle’s cooling system, designed to manage coolant expansion and maintain stable pressure during engine operation. Commonly used in Ford Fiesta models like the Mk5 (2002–2008) with 1.4L and 1.6L petrol engines, it stores excess coolant as temperatures rise, preventing overflow and pressure surges, then returns coolant to the system as the engine cools. Constructed from durable, heat-resistant plastic, it features a translucent body for easy visual monitoring of fluid levels and a pressure-rated cap (typically 15–16 psi) to ensure system integrity. With a capacity of approximately 1–1.5 liters, it integrates seamlessly into the engine bay via OEM-specific mounting points and hose connections. This header tank minimizes air pockets, reduces coolant evaporation, and prevents overheating, protecting critical components like the radiator, water pump, and thermostat. Its corrosion-resistant design and secure fittings ensure long-term reliability, making it essential for maintaining efficient engine cooling in daily driving and varying weather conditions.