I agree with Snowtoy, fix the overheating issue first, then move on to an electric fan.  Don't try to fix something by masking it with a more powerful fan.  Pop the radiator cap and see when the thermostat opens, if it is opening, to see if the water swirls, to see if your water pump is working good.  Also, if not sure on the thermostat, then pull it out and boil it in water and see if it opens and closes by boiling it, then running it under cold water to close it.