Nope, car engines are not run near full output all day long. Truck use is far different. Try running that car at 3/4-full throttle for 10 hrs a day and then tell me it is the same.
I have put mine through pull for 45min full throttle at speeds below 25 MPH, what car does that?
Trucks require airflow for the ATA,condenser, and radiator, all are independent needs.
My '83 originally had a viscus drive and it was missing when I bought the truck (fan driven all the time).
I had a 6.9 service truck that had a viscus fan and you could hear it lock up and unlock during the day. I was pushing that truck hard, 12Klbs for the truck and towed a tandem axle trailer also, It didn't get any better fuel mileage than the L 10 semi either, but the semi was moving 4x the weight and much more wind resistance.
Viscus can work, but it wouldn't be my 1st choice. On my 83 I went with a Horton, because I had one handy. I've had good luck with Bendix, and it would be my 1st choice, as it fails safe (no air, spring applied ). Also had an electric clutch (Facet) on a 3406B that worked ok, took small trailer wheel bearings and seals, but parts became hard to come by as they quit making them when "computer contols" came out, The coil would put quite the "kick" back into the electrical system when the relay opened.
Kysor front air, can be adapted to any fan drive not drilled for rear air, so is another option for replacing viscus or Facet.