The fan will shut off when cool, no wasting fan life or battery. I have 75 with the cats under the hood, while driving the fan does not come on, all the fresh air moving thru it keeps it cool. After I stop and shut it down the heat builds up under the hood with no way to move it out, I then have the vapor lock issue of restarting. It runs fine after it gets going and the aux fan shuts off again when I drive.