Genuine OEM Volkswagen Coolant Expansion Tank, part number 3D0121407H. This reservoir is a vital part of the engine cooling system, designed to hold excess coolant and allow for its thermal expansion and contraction. Weighing approximately 0.982 kg, it ensures proper coolant levels are maintained. Genuine OEM expansion tanks are manufactured from high-quality, heat-resistant plastics to prevent cracking and leaks, ensuring the integrity of the cooling system.