my car is overheating at stops low gears. i turn on the heat and it goes down high speeds im good. ol i checked the fans and they work, i dont see leaks or puddles under the car even after i let it run hot for 20 minutes. but heres the thing that got me real confused i fill up the radiator with fluid and the reserve ad recomended about a gallon of fluid i have put in the past 2 weeks. and everytime i check the fluids when it overheats its bone dry. i did buy the car used so im still figuring out whats wrong with it. could it have been that bone dry that its taking all the fluids? any and all help is appreciated. thanks in advance.