The Nissens Engine Coolant Expansion Tank - 996272 is a replacement part for a vehicle's cooling system. It is designed to store excess coolant that is created when the engine heats up, and then release it back into the system when the engine cools down. This helps to maintain the proper level of coolant in the system and prevent overheating. The tank is made of durable materials and is designed to fit seamlessly into the vehicle's existing cooling system. It is a high-quality product that is built to last and ensure the efficient operation of the vehicle's engine.