Abstract: The method of removing hot liquid coolant from an internal combustion engine cooling system, which includes a radiator having a by-pass outlet, the method including applying suction to the by-pass outlet to draw a by-pass stream of hot fluid, including hot pressurized gas, from the radiator, thereby to reduce fluid pressure in the radiator; and then opening the radiator for safely removing hot liquid coolant therefrom; The removed liquid may be disposed of or treated in a zone or zones outside the cooling system; and returning the treated coolant liquid may then be returned to the cooling system.