Genuine OEM Audi Coolant Reservoir Breather Line, part number 4K0121081CK. This line is crucial for regulating pressure within the cooling system by allowing air to enter and exit the coolant reservoir. It connects directly to the coolant expansion tank, facilitating proper fluid dynamics. Weighing approximately 0.05 kg and measuring 0.615 meters in length, this line is designed for precise fitment. Choosing a genuine OEM breather line ensures the correct material composition and internal diameter, preventing leaks and maintaining the integrity of the cooling system's pressure balance.