Genuine OEM Audi Coolant Hose, part number 420121109A. This hose is designed to connect the coolant system to the expansion tank, facilitating the flow of coolant and maintaining system pressure. It is positioned to connect directly to the expansion tank within the engine cooling circuit. Weighing approximately 0.123 kg and measuring 0.257 meters in length, it is a precisely molded component. Using a genuine OEM coolant hose ensures the correct material composition, pressure resistance, and exact routing geometry, which are essential for preventing leaks and ensuring reliable engine cooling.