The techniques outlined in this SAE Recommended Practice were developed as part of an overall program for determining and evaluating fuel consumption of heavy-duty trucks and buses, but it is applicable to off highway vehicles as well. 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, oil coolers, and others. 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 system’s power consumption for engine cooling systems using fixed ratio, viscous or speed modulating, and mechanical on/off fan drives including electronically activated fan drives. This power consumption may then be used in determining engine net power per SAE J1349. For fan power/speed relationships, refer to SAE J1339.