Genuine OEM Audi Coolant Expansion Tank, part number 8Z0121407A. This component stores excess coolant and provides a reservoir for thermal expansion and contraction within the engine's cooling system. It helps maintain optimal coolant levels and system pressure. Constructed from durable plastic, it weighs approximately 0.26 kg. Choosing a genuine OEM expansion tank ensures precise fitment, proper pressure relief, and long-term resistance to coolant chemicals and temperature fluctuations.