A Coordinating Research Council (CRC) cooperative program utilizing seven North American diesel-powered vehicles (four passenger cars and three heavy-duty trucks) and eight fuels (three base fuels and five flow improver additive-treated versions of the base fuels) was run in Kapuskasing, Ontario, Canada, between January and April 1981. Minimum operating temperatures for each vehicle-fuel combination were determined and compared with predictions from laboratory tests. Significant differences among vehicles were found and related to fuel system design. The use of flow improvers permitted some vehicles with some fuels to operate substantially below the fuel cloud point. None of the laboratory tests predicted the performance of all fuels in all vehicles, but the LTFT (Low-Temperature Flow Test) and the WPI (Wax Precipitation Index), an empirical relationship combining cloud point and pour point, offered promise.