Genuine OEM Audi Additional Coolant Expansion Tank, part number 3D0122407. This component serves as an auxiliary reservoir within the engine cooling system, providing extra capacity for coolant. It helps manage coolant volume changes due to thermal expansion and contraction, ensuring the cooling system operates efficiently. Weighing 0.552 kg, this tank is manufactured from durable, heat-resistant plastic. Choosing a genuine OEM expansion tank guarantees proper material integrity, correct pressure relief characteristics, and precise mounting points, which are critical for preventing coolant leaks and maintaining system pressure.