So yesterday I posted that my MPG was consistently. Driving home,however, the MPG was fluctuating between 7.0 to 99.9 MPG, and I was driving at 60-65 MPH on the Washington DC beltway, which is not up and down hills or in and out of curves. I had filled the tank yesterday morning and the pump cut off at almost 10 gallons, so I forced a full 10 gallons in the tank. Did I over fill ? Could this be why the MPG fluctuated so much ? It did the same thing this morning on the way to work. Mileage between home and work = 22.