I have a 2004 Hyundai Elantra that is overheating. I replaced the thermostat and it did fine on a short 30 mile trip. However on the way home with in 10 minutes it started over heating again. I pulled over, let it cool down because of the steam bath, refilled the radiator with water to make it home. I kept the speed below 50 mph and had no more problems for the rest of the trip. I have 2 fans and only one will kick on when I turn on the ac. I ran a jump wire and it did not come on. Could it be overheating because of only one fan working? I also heard it could be the radiator cap, is this true? Because it only does it at high speeds can it be the water pump