The Ford Fiesta Expansion Tank Coolant (Part Number 17137795854) is a critical component of the cooling system in Ford Fiesta models produced between 1989 and 1997, including the Mk3 (1990–1997). Designed to manage coolant expansion and contraction, it stores excess coolant as the engine heats up, preventing over-pressurization of the system, and returns coolant as temperatures drop to maintain optimal levels. Constructed from durable, heat-resistant plastic, it features a translucent body for easy visual monitoring of coolant levels and a pressure-rated cap (typically 0.9–1.1 bar) to ensure system integrity. With a capacity of approximately 1–1.5 liters, it integrates seamlessly into the engine bay via OEM-specific mounting brackets and hose connections. This tank minimizes air pockets, reduces coolant loss through evaporation, and safeguards against overheating, protecting critical components like the radiator, water pump, and engine block. Compatible with 1.1L, 1.3L, and 1.4L petrol engines common in this era, its corrosion-resistant design ensures longevity in daily driving conditions. Note: Verify part number compatibility with your specific model year, as variations may exist.