Last few fill ups my CONS was actually 3 MPG lower than my calculated. Everything I have read says it should be about 5% higher. Last fill up, CONS showed 49MPG, my calculated was 52MPG (All highway at 73mph and AC on Vegas to LA)
What is full? 10.2' 9.85 10.6 or anything around there. My point is that if you even had a wide open calibrated container and you stopped the pump at ONE gallon, it would still be wrong for multiple reasons. Is the pump accurate? How much gas is still in the hose? Is the mandatory temperature control system in the gas station tank accurate? I have only touched the surface. But instead of concerning yourself with gasoline used, think about how to do better. On one trip to LV from Sacto with my 2005 , I got 69 mpg! Admittedly There was a hellashus wind coming form LA on I 15. This PIP is magic and there are multiple ways to reduce consumption.
I use Fuelly to track all my fills ups. You can see the info in my link. Andy, I would love to see you get over 50mpg OC to Vegas in 110 heat. I guess I could have set the cruise at 60 mph and dodged the bullets from pissing people off. I don't like to hypermile, I'll spend the extra $2 in gas. Point of this thread was that most people have stated that the CONS is 5% over actual, and I am seeing the opposite.
Last weekend i went from San Diego to LV in 114 degree heat blasting my A/C the whole way, doing 75-80MPH most of the way, and I got 48MPG there, and 49MPG back. This car is like magic!
Please don't misunderstand me, I think the last two posters are doing great! But further records will happen.
Only way to get better mileage is to travel to LV on a party bus (which is what we did for an Aztecs game earlier this spring!)