That was how it went with my accord. I thought I had a 13 gallon tank, read the manual and it said 16.9 gallons. Same with the dsm now, I keep filling it at around 12.5 gallons, but now I read that I have a 16 gallon tank (I'm about to go ask if this is right). Easiest way to figure out might just be to carry a gallon of gas with you and run it dry, run it a bit of that gallon at a time to the nearest gas station and let it idle off the rest. Fill it up and see what it takes. I'm tempted to try it out.