An analysis based on forced-convection heat-transfer theory, similar to the analysis presented for air-cooled engines in NACA Report No. 612, is made of the cooling processes in liquid-cooled engine cylinders. Semi-empirical equations that relate the average head and barrel temperatures with the primary engine and coolant parameters are derived.

As a supplement to an investigation of the cooling characteristics of a multi-cylinder liquid-cooled engine, tests were conducted with two liquid-cooled cylinders in order to isolate the effects of the various engine and coolant variables on cylinder temperatures and to obtain engine-cooling data required for a fundamental study of the heat-transfer processes in liquid-cooled engines.

A study has been made of the heat-transfer processes in liquid-cooled engines and an equation has been developed that relates the heat rejection to the coolant and the engine operating conditions. Tests of an Allison V-3420-11 engine have been made to check the accuracy of the equation and to establish the cooling characteristics of the engine. By determining the few constants of the equation, the heat rejection to the coolant may be predicted with good accuracy for any particular engine operating condition. The tests showed that the rate of heat dissipation to the coolant was only slightly affected by either the rate of coolant flow or the relative proportions of ethylene glycol and water composing the coolant mixture.