98chevy2500SS
Specializes in Accessories 101
I believe the auxiliary fans only came on 8600-up GVWR trucks. Mainly seen them on one tons. My dad's dually has the aux fan, trans cooler, and power steering cooler (I think that's what it is? I could be wrong). Like others have said, I would assume it's to cool things down when you are towing something for long periods of time.