Accurate fuel fill without topping off?

[sbergman27]

Originally Posted by docB

Filling to the very top is nice if you have all the time in the world. Plus you are hauling the weight of that extra fuel.

Well... That extra 1.1 gallons of fuel gets me an extra hour (or so) down the road before the next refill. So on a "time economy" basis that doesn't make sense. However, on a time spent out in the cold and whistling wind" basis it might, since a fuel stop involves substantially more time than just the pumping time. (Exit, find the station, find a pump... etc. etc. ... update the scangauge, get back to the highway, get back up to speed...) But the time spent out in the cold is significantly increased. And I really, really don't like the cold.

Gasoline weighs about 6.5lbs/gal. So 1.1 gallons weighs about 7lbs. Or about 0.25% of the weight of the car (with me and my suitcase in it). Of course, the *average* added weight over the course of the tank is half that, or about 0.125% of the weight of the car. And on the Interstate, wind resistance dominates. The difference made by the extra weight works out to about 0.02 mpg.

However, despite the humorous flights of fancy in the public service announcement, there are enough rational reasons not to top off that I've switch to filling at the pump's slowest setting and then pumping as much as I can by pulling the trigger *ever so slightly*, just once to make sure that the automatic mechanism got it right the first time. It doesn't work out to more than 0.1 gallons more. And the method seems to give me a consistent adjustment factor on the scangauge.

-Steve