Genuine OEM Audi Thermostat Housing, part number 03H121121D. This component is crucial for the engine cooling system, housing the thermostat and regulating the flow of coolant. It is typically located on the engine block or cylinder head. Constructed from durable plastic, it is designed to withstand engine temperatures and pressures. Using a genuine OEM housing ensures precise fitment and proper sealing, preventing coolant leaks and maintaining engine thermal efficiency.