Genuine OEM Volkswagen Engine Coolant Reservoir Hose, part number 3C0121109AD. This hose connects the coolant reservoir to the main cooling system, ensuring proper circulation and maintaining optimal fluid levels for engine temperature regulation. It is a vital part of the engine cooling circuit. Weighing 0.2375 kg, this genuine OEM hose ensures correct routing geometry and resistance to extreme temperatures and pressures, preventing leaks and maintaining efficient cooling system operation.