Genuine OEM Volkswagen Expansion Tank Cap, part number 1C9121321. This essential component seals the coolant expansion tank, preventing coolant loss and maintaining the precise pressure required for optimal engine cooling system operation. It features a clear coolant symbol for easy identification. Made from durable, heat-resistant plastic, it is designed to withstand the demanding conditions of the engine bay. Using a genuine OEM cap ensures the correct pressure rating and a secure seal, critical for preventing overheating and maintaining engine longevity.