Genuine OEM Audi Coolant Hose, part number 4E0121109L. This hose is crucial for maintaining optimal engine temperature by facilitating the flow of coolant between various components within the engine cooling system. The diagram indicates it connects to the coolant expansion tank. Constructed from durable, heat-resistant rubber, it measures approximately 0.255 meters in length. Choosing a genuine OEM coolant hose ensures the correct routing geometry, material composition, and resistance to thermal cycling and pressure, preventing leaks and premature failure.