Abstract: A reduction of hot spots in the combustion chambers and the simultaneous elevation of bore temperature in an internal combustion engine are achieved by a boiling liquid cooling process in which a high molecular weight, high saturation temperature organic coolant is supplied to the coolant jacket of the engine head entirely in the liquid state, thereby greatly reducing the ratio of vapor to liquid in the head jacket for more effective heat transfer from the head to the coolant.

Abstract: A cooling process for an internal combustion engine comprises the steps of mechanically pumping a boilable liquid coolant having a saturation temperature above about 132.degree. C. at atmospheric pressure from the engine coolant jacket through a radiator and back to the coolant jacket, continuously removing by substantially unrestricted convection through at least one outlet in the highest region of the head portion of the coolant jacket substantially all gases other than those that condense in the coolant jacket, conducting gases from the outlet to a condenser, and returning condensate from the condenser to the coolant jacket. Cooling apparatus comprises a liquid cooling circuit and a vapor discharge and condensation circuit adapted to carry out the process.