When you mention your gas mileage, how do you figure that out? How can you be so accurate? Even if you try to use the gas light as an interval( the miles accumulated till the gas light comes on) you still wouldn't know exactlly how many gallons of gas you've burned. Unless you drive it till the last drop then you divide that by the capacity of your tank ( 13.6) you can't be that accurate.

Filling up the car when the light comes on then sustract that amount from the total capacity(13.6) doest not help either. Simply because the amount flactuates considerably, even though I fill up immediately within mile or two
after the gas light comes on. How much does it flactuate? Up to two 2 gallons sometimes!

On a recent trip I noticed that it takes around 9 gallons to fill up my tank in other states vis a vis 11 & up in CA !!! how accurae are those damn pumps!