<div class="htmlview paragraph">INCREASING engine outputs have required methods to control the piston temperature. The work presented in this paper shows one successful means through the use of a piston of low conductive, correlated with an appropriate rate of piston cooling oil from the engine lubrication system.</div> <div class="htmlview paragraph">The effects of coolant temperature, load, and speed over the propeller load curve, and a piston baffle, on piston temperatures are investigated by thermocouples silver soldered in a 6 x 6½-in. diesel, two-cycle piston. Tests indicate that the rate of cooling oil does not have to be excessive to secure adequate cooling. Substantiating data from an 8 x 10-in. diesel engine are given.</div> <div class="htmlview paragraph">Steel piston designs for use with jet oil cooling are shown. These are for the 6-in. diesel on which most of the data for the paper were taken.</div>