I hope I can explain this. Engine driven pulls about 4,000 CFM through the radiator at speed (about 3,000 RPM). This is important at low vehicle speeds. But if you are going 60 MPH it really doesn't do much of anything but spin so they put a fan clutch on. It still spins but not as fast and really at 60 do you need a fan? And it takes power to run this fan plus it puts stress on the water pump its bolted on.
Electric fans have been on most cars for years and the newer ones are variable to lesson engine load even more and really the only time you need a fan are speeds less than 35ish.
I don't have exact numbers but some data from the truck side suggests and it should be accurate about a .3 increase in MPG and about 2 in HP.
I am working with AFCO | Racing Parts | Performance Parts | AfcoDynaPro.com
to have them make me one. I just need to get my hands on a shroud to send them.
I did Law Enforcement for about 10 years the best thing to ever happen was an electric fan on the car. I also went by the Ford garage and talked to them and the mechanic was "why wouldn't you want a electric fan". The bigger chassis are exempt from fuel standards so there is no reason for Ford to put electric fans on them but if you look at the big rigs and most construction equipment it all has electric fans.
Also if you still have a heat issue say you do a lot of mountain driving, you can add a pusher fan to help a bit.
I hope that helps. Even a 1/10 increase on MPG and a modest 1.5 increase in HP and torque would be huge when your sucking a gallon every 9 miles.
I asked AFCO for a WAG for a turn key kit. My radiator is a down flow about 35 X 32 if I remember right two bolts and two tabs for the shroud and about 8 for the fan and clutch.
I have searched for a kit and just haven't found one and I hate the noise when the fan clutch locks and spins that big fan.