The only things to consider are:
* Your truck probably came with a fluid clutch fan. While it was still pulling energy, I doubt it was "0.11HP" all the time.
* Your electric fan gets its energy via the alternator. The 0.11HP it consumes is magnified by whatever your electric system efficiency is (i.e. 0.11HP may actually be 0.15HP).
You will definately see better mileage (no idea how much, though). I just wonder how long the fan will take to start making you money. My guess is that you won't turn a profit for a few months, but it should help in the long term.
I'm just anal, but I find it valuable to calculate overall costs. We've all heard of the guy driving 15 miles for gas 5c cheaper.
- LostCause