Gentlemen,

I am experiencing a significant variation of gas mileage, from 22mpg-35mpg. I understand that differences in driving style, tire size, city v hwy driving, ac\heat and brand of gasoline contribute to how efficient the Fit is.

But, one variable I have not found an answer to is, is if the fuel top off point consistent? If the gas tank tops off at different points with each fuel up, how can I be sure I'm getting the most accurate read of my fuel efficiency?

What about variations of the pump? Atmospheric pressure? How can I be sure that I'm getting a consistent read?

2010 Sport in the city: 24mpg, Hwy: 30-35mpg.

 

Your fuel top-off point will not affect your mileage.. Temperature v. density will affect what you get in terms of mass at the pump, but assuming the pumps are all calibrated properly 1 gal = 1 gal.

Density/Temperature will affect the mass of that gallon though.

But again the fill capacity of the tank has nothing to do with your mileage fluctuations.

Stick with one station, preferably even the same pump and the same grade of fuel.

Then watch as your driving habits, commute and weather skew your mileage. Sitting at a stop light you effectively are getting 0mpg.

 

^^like he said^^
The other thing you can do to get a better handle on MPG is to fill the tank and write down the odo mileage. Then simply keep track of the number of gallons you put in the tank at each visit to the pump for a few times. then, on the calculation day fill it up and record the miles on the odo [not the trip, but you can use it if you don't forget and reset it]. Now add up all the gallons and divide it into the mileage and you've got a representative MPG on your car as you drive it. Like DSM says, using the same pump at the same station for the first and last fill-ups essentially guarantees accuracy.

I would be curious to know the calculate to on-board mpg comparison. Mine is usually within 1.5mpg but it depends a lot on local/highway mix on the measurement.

 

While I try to keep consistent with the same station\pump, I've been traveling and unable to stay loyal to my local watering hole.

Perhaps I wasn't very clear with my question: How can I get an accurate calculation (miles driven\gallons filled) if the top off point of the fuel tank is a little higher or lower than the previous fill up? Is there enough variation to really change the final number of my MPG?

 

The fuel top off point difference between one pump and another is so small you probably wouldn't be able to measure it when working your MPG. I second the writing your odo mileage down idea. My father has been doing that since he picked up his PT Cruiser since may 2001, and has entries to every single time gas was put in that car. It's neat to look at the prices go up and down and look at the date when gas was put in it (Katrina, 07 and 08 gas hike). The first entry was when he paid 1.23 for a gallon of gas waaaaayyy back in '01.

 

I use an app for my phone called gasuplogger Windows Mobile 6.5. im sure there are things out there for Andrioid, iOS or WinPhone7 Probably for free.

~SB

 

I have an Android phone (NexusOne) and use Mileage to do my tracking. Does everything I need and more. I've been using it for a long time and it works great.

Here's the link if youre interested.
https://market.android.com/details?i...=search_result

There are others but I havent really had a need to change.

 

Actually, it's a fairly big difference if you're not putting in much fuel. For example, suppose you drive 100 miles and put in 3.3 gallons of gas. Your computed mileage is 30.3 mpg. Maybe another pump lets you put in a little more, like 3.5 gallons (I've pumped more than 0.2 gallons in after the pump clicks off). When you compute your mileage, you'd get 100/3.5 = 28.6 mpg.

You can minimize the error by putting in lots of gas at once (if it was 300 miles and 9.9 gallons of gas versus 10.1, the difference is 30.3 mpg vs. 29.7 mpg)... or just don't rely on a single tank MPG.