The Engine Coolant Overflow Reservoir is a component used in vehicles to store excess coolant that expands as the engine heats up. It helps maintain the proper level of coolant in the radiator and prevents overheating. This reservoir is specifically designed for coolant overflow purposes in automotive cooling systems. This reservoir is new and has not been used. The box has been open. Please see the pictures for details. If you have any questions, please feel free to ask. Thank you.