Reading through the manual for my Exploder, Ford suggests that when using 4x4 on paved roads it should be the wet rainy conditions. Does anyone know the technical reason(s) why?

 

If the tires have too much grip, the 4x4 trans bits will give out. The system (at least this was the case when I blew my Jeep 4x4 case) needs to have the tires slipping. Lock it in 4x4 mode on dry pavement and drive in a circle. The front will want to hop since the wheels are turning at different rates. If it didn't hop, you'd break something.

John -- who's not a 4x4 expert, but has experience wrecking a transfer case.

 

John is right, the transfer case wants to bind if everything is not turning exactly equally, so it is hard on the gears/chain instead of the tires. Some transfer cases are viscous and it eliminates the issue. My wife drives an Exploder, but it is full time AWD.