Genuine OEM Volkswagen Coolant Regulator Housing with Thermostat, part number 03L121111AC. This integrated assembly plays a critical role in the engine cooling system by housing the thermostat and regulating the flow of coolant. It ensures the engine reaches and maintains its optimal operating temperature. Weighing 0.295 kg, this housing is typically made from high-strength plastic or metal, designed to withstand thermal cycling and pressure. Using a genuine OEM housing with thermostat ensures precise temperature control, proper coolant routing, and long-term leak-free operation, essential for engine longevity.