The technique outlined in this SAE Recommended Practice was developed as part of an overall program for determining and evaluating fuel consumption of heavy-duty trucks and buses. It is recommended that the specific operating conditions be carefully reviewed on the basis of actual installation data. Cooling requirements are affected by all heat exchangers that are cooled by the fan-drive system. These may include radiators, condensers, charge air coolers, or oil coolers. Because of the variation in size, shape, configuration, and mountings available in cooling fans and fan-drive systems, specific test devices have not been included. Using known power/speed relationships for a given fan, this procedure can be used to calculate the fan-drive systems power consumption for engine cooling systems using fixed-ratio, speed modulating, and on-off fan drives. This power consumption may than be used in determining engine net power per SAE J1349. For fan power/speed relationships, refer to SAE J1339. The purpose of this document is to provide a recommended method for determining and comparing the power consumption of fan drives over a variety of operating conditions. The resulting power consumption data is useful in predicting the fuel consumption of engines using these fan drives and in comparing one fan drive to another on the basis of power consumption. There is no known comparable ISO specification.