The effects of engine speed, load, and injection timing on the distribution of heat rejection to the coolant were examined in a single-cylinder divided-chamber diesel engine. The cooling system was separated into four zones: cylinder liner, intake port, exhaust port, and ante-chamber. The fractions of the total amount of heat rejected to the coolant from the four cooling zones were moderately affected by load and injection timing, but were not affected by engine speed. Typical values of these fractions are: cylinder liner - 53%, exhaust port - 22%, antechamber -18%, and intake port - 7%. The total amount of heat rejected to the coolant increased with engine speed and load; injection timing had a smaller but significant effect. Finally, the heat rejected to each cooling zone was correlated with the rate of fuel consumption.