Shop Coolant Tank Caps. Order Coolant Reservoir Cap & Coolant Overflow Tank Cap. Explore Coolant Recovery Tank Cap. Find Coolant Reservoir Caps Replacement Cost. Regular inspection of your vehicle's coolant tank cap is crucial for ensuring the integrity of the cooling system. If you notice coolant leaks, steam from the hood, or an overheated engine, it's time to consider a replacement. When selecting a new cap, choose one made from durable materials designed to withstand high pressure and temperature fluctuations. Options include thermoplastic or metal caps, with features like safety release mechanisms. Proper installation is straightforward—simply twist and secure the cap to maintain optimal pressure levels and prevent coolant loss, keeping your engine cool and your sales hot.