Water Tank Expansion Bottle compatible with W163 M Class models including ML350 and ML500.Designed to function as a replacement coolant reservoir, this tank connects to the vehicle's cooling system to accommodate thermal expansion and maintain proper pressure.The unit is constructed to match specifications for shape, size, and connection points.Includes necessary fittings for installation.Ensures stable of the engine cooling under varying temperature conditions. This is not an part.All brand mentions are used strictly for compatibility reference.