Just back form a 1500 mile trip in the 6000 lb family car (2003 dually 4 door) and I have an obeservation about the clutch fan:
The truck temp hovers at 200 degrees and the clutch fan sometimes kicks in when I'm cruising at 60+ it goes off after a few minutes. Assuming this is normal that means that 60 mph does not deliver enough air to keep the engine cool (outside temp around 100 F)
Every square foot of open grille equals 5000 CFM at 60 MPH so an electric fan would have to move north of 10,000-15,000 CFM to equal that, right?
Oh yeah, i got 19.9 miles on the best 350 leg of the trip (not hurried, rested, no traffic) I got 18-19 on the rest of hte trip.