Genuine OEM Volkswagen Coolant Regulator Housing With Thermostat, part number 03L121111AE. This assembly is critical for regulating the engine's coolant temperature by controlling the flow of coolant through the radiator. It houses the thermostat, which opens and closes based on coolant temperature. Located within the engine cooling system, this component ensures the engine operates at its optimal temperature range. Genuine OEM parts guarantee the correct thermostat calibration and housing seal for reliable engine performance.