Is there a float in the tank that monitors fuel level? My book says i have a 17 gallon tank. When i am on empty I can fill it up with $20, wich is less than 10 gallons. I wrote down the mileage when I filled it up to see how many miles till it hit empty again. Only 116 miles from F to E. Also when im driving the gas needle is constantly changing. Is this something hard to fix?