No, because the general idea behind efficiency has to do with the costs that are incurred to achieve a particular outcome. For example, a method is said to be more efficient than another if it achieves the same outcome at a lower cost. The outcome in the case of cars is movement because that's the purpose they're built for, so a measure of car efficiency has to reflect how costly is to move the car some unit of distance. The RPMs the radiators fans do per mile don't tell us anything about how costly it is to move the car, therefore, no, it's clearly not a good efficiency measure.