Genuine OEM Volkswagen Coolant Expansion Tank, part number 1EA121407H. This tank holds excess engine coolant, allowing for thermal expansion and contraction while maintaining proper system pressure. It is typically located within the engine bay, connected to the radiator and engine block. Constructed from durable, translucent grey plastic, it allows for easy visual inspection of coolant levels. Choosing a genuine OEM expansion tank ensures precise fitment, correct pressure relief valve calibration, and long-term resistance to heat and chemical degradation.