Genuine OEM Audi Coolant Reservoir, part number 7M3121407B. This component is designed to store excess engine coolant, accommodating the expansion and contraction of coolant volume as engine temperatures fluctuate. It also serves as a fill point and allows for visual inspection of coolant levels. Weighing 0.534 kg and measuring approximately 0.2m in length, it is constructed from durable, heat-resistant plastic. Using a genuine OEM reservoir ensures proper pressure regulation, leak-free operation, and compatibility with the cooling system, preventing potential engine damage from overheating or fluid loss.