Genuine OEM Hyundai Coolant Reservoir Tank Assembly, part number 25430CO000. This component serves as an expansion tank for the engine's cooling system, storing excess coolant and allowing for fluid expansion and contraction due to temperature changes. It helps maintain proper coolant levels and system pressure. Located in the engine bay, it is connected to the radiator and other cooling lines. Using a genuine OEM reservoir tank ensures correct capacity, durable material construction, and proper sealing, which are crucial for preventing coolant leaks and maintaining the efficiency of the engine cooling system.