Genuine OEM Volkswagen Coolant Reservoir, part number 4M0121403F. This component stores and manages excess engine coolant, playing a crucial role in the engine's thermal regulation. It is typically located within the engine bay, often mounted near the radiator. The reservoir is constructed from durable plastic designed to withstand engine temperatures and coolant pressures. Genuine OEM parts ensure precise fitment and material integrity for reliable long-term operation.