step 108 ensues in which the parameter u03b4t which determines the time span in which the reference or maximum temperature should be reached is set at a predefined value u03b4t harvesting if it is determined in step 106 that harvesting is underway step 110 ensues in which the parameter u03b4t is set at the value x u00b7 u03b4t harvesting the parameter x is selectable and is as a rule less than 1 since the dissipated energy of the engine is greater when harvesting than in roadway travel and therefore the required cooling capacity must be made ready more quickly nevertheless cases are also plausible in which x is greater than 1 subsequently based on the temperature differences and the ambient air temperature sensor 44 at input 34 the determination is made in step 112 as to the amount of air necessary to be fed in order to offset the temperature difference in this step 112 it can be meaningful to measure both the temperature of the ambient air in front of the fan 20 and the temperature of the air that has flowed past the cooling device 12 in this manner u2014 and in consideration of the known air flow rate of the fan 20 u2014 the quantity of the dissipated heat can in each instance be determined as a function of the temperature of the coolant and the ambient air temperature therefrom it is possible to determine the quantity of air that is required to dissipate a certain amount of heat from the cooling device 12 when one knows the temperatures and the quantity of ambient air needed to dissipate a certain uniform amount of heat calculation of the given amount of ambient air required is possible it would also be plausible to store.