If you're riding it that long and the fan isn't comming on I would say that you have a faulty coolant temperature sensor, Its a little plug in your radiator with an electrical wire going back to your fan, once your coolant hits a certain temperature it instructs the fan to turn on. As far as riding it, I wouldn't worry to much, as long as you've got air moving across the engine. I would give it a good break every 30-45 min. and you shouldn't have any problems. Also make sure you don't take it through any water that would touch the engine while it is hot or you could crack the block.

 

It may not even be the sensor, because it may be the fuse to the fan that has gone bad.If you open up the little fuse box there should be an extra fuse right next to the one that is in use.Dont ride the quad if you dont want water pump problems either.The fan is supposed to cool the antifreeze and if it is not cooled enough it expands and it will break the seal on the water pump.