I too would like to add/install an electric fan. But my first concern is: how much power is it draining from the alt, and how much 'reserve' does the alt have to power the fan? especially when the truck is only idling?, wouldnt that cause and unusal amount of battery drain? Please help...

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2000 XLT Silver 5.4L SC 4X4 ORP 157"wb Ford Floormats, Mudguards, lighted emblems, lighted interior door handles(all 4) Chrome Grill (4x2 style), Diamondplate bed caps, Pro-Tech tool box, Air Box mod.

 

I wouldn't worry too much about the alternator, if you have the tow package, the heavy duty alternator is rated at 130 amps.The flexalite 210 draws 20 amps, which is less than a sixth of it's capacity. Modern alternators can put quite a bit of current even at idle.

 

I second Bill_Aquino's post. Your battery will make up for any load difference your alternator can't supply. Your truck’s alternator should have more the enough capacity to cover the load of your ignition, lights, wipers, blower, and accessories at idle to allow you to add a 20 AMP fan with no trouble. Keep in mind that a few members of this board have added multiple off road driving lamps that are capable of drawing more than 30 AMPS.

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99 4X4 XLT S/C with ORP
5.4L 3.73LS
Flow Master Dual Exhaust
K&N Filter w/ Intake Mod
Flex-a-Lite Black Magic 150 Electric Cooling Fan
Jason "Hugger" Truck Lid

 

Think of all the little imports with 60A alternators.
Most have electric fans.
Our trucks have very high capacity alternators compared to most cars.