The effect of fuel cetane number on low temperature starting, white smoke, and noise has been determined for two light-duty diesel vehicles. Over 400 low temperature (≥-17°C) starting tests were conducted in a temperature controlled test facility with fuels ranging from 26-61 cetane number. Results show that both vehicles exhibited satisfactory starting and warmup on a fuel having a cetane number of 40, the ASTM specification minimum. Above 40 cetane, both vehicles were relatively insensitive to changes in cetane number; a decrease in fuel cetane number from 45 to 40 affected starting and warmup performance only slightly. Addition of cetane improver to a low cetane number fuel decreased noise and smoke to a level comparable to that of a fuel with equivalent natural cetane number. Engine design factors, including glow plug operating cycle and low temperature cranking speed, significantly affect low temperature startability.