Radiator Coolant Expansion Tank and Hose compatible with E46 3 Series models from 1998 to 2007.Includes part numbers 17117573781, 17127510952, 11531436408, and 17137524812.Designed to hold excess coolant and maintain proper cooling system pressure.The tank connects to the engine via a hose to allow thermal expansion and contraction of coolant during.Mounts securely in the engine compartment and integrates with the existing cooling system.Suitable for replacement or repair applications.