Do a search on "aux fan" and you'll get lots of info. Several of us discussed this in depth last week. You will learn about the two speeds of the aux fans. Only the high speed is related to coolant temp, and even there it is set to come on about 107 degrees on most models, so you may not actually have an aux fan problem (though you may have an overheating problem).
ALso, the mechanical fan (driven by the engine) has a thermostatic clutch which often goes lame. Might also search on "fan clutch."