Genuine OEM Volkswagen Coolant Expansion Tank, part number 3Q0121407A. This vital component in the engine cooling system holds excess coolant, allowing for thermal expansion and contraction of the fluid. It also helps maintain proper system pressure, preventing cavitation and ensuring efficient heat transfer. Positioned within the engine bay, it is typically made from durable, heat-resistant plastic. Weighing 0.707 kg, this tank is designed for specific volume and pressure ratings. Using a genuine OEM expansion tank ensures correct material composition, pressure relief valve calibration, and hose connections for reliable engine cooling and longevity.