Genuine OEM Hyundai Coolant Reservoir Tank, part number 25430J7400. This tank is a crucial component of the engine cooling system, designed to store excess coolant and allow for expansion and contraction as the engine heats and cools. It helps maintain proper fluid levels and system pressure, preventing overheating. Using a genuine OEM reservoir tank ensures correct material resistance to coolant chemicals, accurate level markings, and a leak-free seal, which are vital for the long-term health of the engine.