Switching to an electric fan would give you better mileage because it frees-up as much as 12 hp. I think that's a big reason so many vehicles have them now.
With such a big difference in mileage posted on this board, I have to believe driving habits and tires are a bigger influence than anything else. I'm doing some testing currently. With a Jet stage 1, cai, flomaster duals, my last talk got 16.5 completely city driving. After the next talk I'm taking the Jet chip off and see if there is a change. When I checked highway mileage a year or so ago I got 21.25. I'll check that again to.

 

I believe that the viscous clutch fan can use over 12 horsepower
when locked up after 220 degree F air has flowed over the little coil in the front of the clutch, and
official support for that from Jeep is found here:

http://www.allpar.com/model/98changes.html

but people need to realize this is at full throttle and 4000 rpm
and that in typical driving at rpm less than 2200
when the viscous clutch is unlocked in air less than 220 F
and the fan blades are slipping in the silicone fluid
the hp used is VERY small....about 1 hp or less.

 

please post all your findings from your tests. Including all your mods, size and type of tires what the psi is in the tires etc. I know I would really be interested in your results.

 

HankL is DA MAN! Wow, what information! Okay, on me '93 3.9 L V6, I get about 19 highway. I don't complain about that. I also have a '96 Chevy 5.7 L V8, extended cab, long bed, and it gets better mileage than the Dakota, almost 20 mpg on the road. But I like driving the Dakota better. Like someone said, I don't think we can complain with the fuel economy so much with what we ask of these trucks. After all, they are trucks, and I use mine like one.

 

Amen, I came up during the 60s&70s-we had some junk back then-my old 2wd pickups ranged from 12+ to 15 they weren't very heavy either.I'm not going to say what an old chevy fulltime 4wd with a 5.7 got.Our trucks are pretty nice-Free erg

 

That's a fairly dramatic increase for a clutch fan, but about right for a flex fan. That was about the change I saw in my '78 Aspen that had a 5 blade flex on it as recieved. That, and some carb tuning, has got me up to about 18 MPG avg. with a 4 bbl. carbureted 318 and 904 trans. FWIW, the car weighs ~3,300 pounds (slightly less than a std. cab4x2 Dakota).

So long as they're working properly. We had a customer with an '05 Durango, about 80K miles. Their fan clutch got loose, thusoverheating. Couldn't get a Mopar clutch for a week, so installed an aftermarket unit. It locked up two days later and took their fuel economy went from 17 to 9. And the vehicle wouldn't exceed 85 MPH, period. A clutch fan that doesn't slip causes a tremendous amount of drag on an engine.

 

With the coming of colder winter temperatures
two Dodge enthusiasts could get together
and do a careful MPG test with two trucks 'convoy' style
in a circular highway trip.

On the first circle of the trip one truck would remove its clutch fan blades (put clutch back in place). At the end of this first stage both trucks would fill up and check their MPG.

On the second stage of the trip, the first truck would put its fan blades back on, and the second truck would take the fan blades off and both trucks would repeat the circular trip.

If two friends were going to a football game out of town, for example
this would be a good opportunity to do a test.

The effect of fans is small
and it takes a careful test to find out something you can trust.

This double truck testing is the way pros do it,
such as the way Goodyear tested its new tires before witnesses in Texas
at the end of this article:

http://www.etrucker.com/apps/news/article.asp?id=60421