Genuine OEM Audi Coolant Reservoir, part number 8T0121405. This component is a vital part of the engine cooling system, designed to hold excess coolant and allow for thermal expansion and contraction of the fluid. It maintains proper system pressure and provides a visual indicator for coolant levels. Typically located in the engine bay, connected to the radiator and engine. Weighing 1.54 kg, this reservoir is engineered for durability and precise fitment. Using a genuine OEM coolant reservoir ensures correct material composition, pressure resistance, and hose connections for reliable cooling system operation.