Many good replies already.

To get the full benefit of an electric fan addition, and most $ return on investment from fuel economy, there should be a switch to turn the electric fan off at highway cruise to lessen un-needed air coming in through the grille and going out the bottom of the engine compartment, then flowing against the rough under carriage.

With the fan turned off the engine coolant temperature should be allowed to rise to at least the 220 to 240 degree F level which also improves part throttle engine efficiency, and heats the air up flowing through the throttle so the throttle blades will open up, improving manifold absolute pressure, and lessening the amount of ‘negative work’ the engine produces dragging pistons down against a vacuum on the intake stroke.

Either a knowledgable human driver, or a well written microprocessor program, should decide when to turn this switch on/off.

On top of this recent Ram trucks have grille shutters to lower harmful airflow at part throttle highway cruise.