Aluminum expansion tanks are commonly mounted as the highest point of the cooling system and used as a fill point on vehicles that have a low mounted radiator or when the fill point on the radiator is not accessible. The 1/2"NPT bottom supply fitting is commonly connected to the low pressure side of the cooling system and the return fitting is connected to a port located high on the engine to help release any air trapped in the system. Tanks feature a machined filler neck to accept most standard radiator caps and a 1/8”NPT port for connecting to an overflow tank.