Genuine OEM Volkswagen Coolant Expansion Tank, part number 7E0121407D. This essential reservoir holds excess coolant and accommodates the expansion and contraction of coolant volume as engine temperatures fluctuate. It plays a vital role in maintaining the correct pressure within the engine cooling system, preventing overheating and cavitation. Constructed from durable, translucent plastic, it allows for easy visual inspection of coolant levels and weighs 0.662 kg. Opting for a genuine OEM expansion tank ensures precise fitment, correct pressure relief valve calibration, and material integrity to withstand thermal cycles and chemical exposure, preventing leaks and system failures.