Genuine OEM Audi Coolant Expansion Tank Cap, part number 3B0121321. This blue plastic cap is designed to seal the coolant expansion tank, also known as the coolant balancing container, within the engine cooling system. It plays a crucial role in maintaining the correct pressure within the cooling system, which is essential for efficient engine operation and preventing coolant boil-over. Weighing 0.0566 kg, it measures 0.08m x 0.08m x 0.04m. Using a genuine OEM cap ensures the correct pressure relief valve calibration and material integrity, vital for reliable cooling system performance and preventing coolant loss.

Catalogue entry: COVER blue.

Fitted with: 2H0121407D TANK, 2H0145830A SOCKET, G12E050A2 COOLANT.