The Horton fan would be able to "disengage" at any time you want as well as engage to keep on when pulling a hill in high temps. the Electric fan will give you more power from not the engine running but is thermostatily controlled unless you wire in a switch to make it run.
all the big rigs (18 wheelers) have the horton kind where it freewheels when not needed
hope this helps
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2001 QC 2500 4x4 bronze W/two tone Driftwood, 24valve HO 6sp. Westin side bars, fender flares, Spray on bedliner, shell Painted to match and soon to get Bf Goodrich AT Tires. Bed rug inside shell W/aux marine deep cycle batt for lights, etc. M Brolins' CB mount.
Name of rig is "big bronze Brute"