Genuine OEM Volkswagen Coolant Expansion Tank, part number 1J0121407F. This tank is a critical component of the engine cooling system, designed to hold excess coolant and accommodate its thermal expansion and contraction. It helps maintain optimal coolant levels and system pressure, preventing overheating. Made from durable, heat-resistant translucent plastic, it allows for easy visual inspection of coolant levels. Weighing 0.344 kg, it ensures proper fitment and long-term reliability. Using a genuine OEM expansion tank guarantees material compatibility and structural integrity under varying engine temperatures and pressures.