Genuine OEM Volkswagen Coolant Regulator Housing, part number 021121117B. This housing contains the engine's thermostat and is crucial for regulating the flow of coolant, thereby controlling engine operating temperature. It is typically mounted to the engine block or cylinder head. Constructed from durable metal designed to withstand high temperatures and pressures within the cooling system. Genuine OEM housings ensure precise thermostat placement and proper sealing, vital for maintaining optimal engine temperature and preventing overheating.