The only way to get ir right is topping up and then after 1,000 miles or so of jotting down amount of fuel purchased top again and make the calculation.

Based on this I found myself getting an average of 43.1 REAL MPG hilly terrain, doing some hypermiling.

The dashboard AVG is off by 12/14%

MMM

 

That makes sense really. Just check your odometer, save your receipts for a few months, check the number on the odometer when you just about run out on the last tank. Then divide. It's probably the most reliable method. I plan on doing this after the break-in period.

 

Yeah, sounds more reliable but a little overkill. I calculate my mileage on almost every tank when I fill up by simply dividing the miles I've driven since last fill-up by the amount of gas the car took. I know this isn't accurate as a one-time calculation but my results end up being so close together and regular that I know for sure I average 33-34mpg in my '08 AT Fit.

 

The big problem with per-fillup calculations on the Fit is its wonderful "magic" gas tank that supposedly holds 10.9 gallons but into which people like me routinely pump 12+ gallons.

I can usually get an additional 2 gallons in the car after the pump kicks off the first time. With that much additional space in the tank, the pump's kick off point becomes a critical factor in determining how much fuel goes in, and hence the miles per gallon you will calculate. Averaging over multiple tankfuls helps smooth that out, if you choose not to 'hyperfill' the tank each time.

 

My view is that the "magic" gas tank factor only ever affects an individual result and since I *only* give a damn about the long term averages I don't sweat it. I guess we're pretty much saying the same thing.

EDIT: If I were trying to be able to say I had achieved a certain high mileage on any given tank (like many on FitFreak) I would probably change the way I calculate my mpgs. :P

 

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That's why I add an extra 0.8 gallons of gas on every fill up shen the pump kicks off. My past MPG tracking on my CR-V showed a reduction in MPG relative standard deviation (rsd) when I added a consistent 1.3 gallons over pump kick off. YMMV.

 

Just recently check the fuel mileage and the car shows 39.X mpg but doing the trip meter and gas pump math it comes out to about 37mpg so the car is optimistic by about 2mpg....I recall it being optimistic like this when the car was new too but back then the fuel mileage was lower I think average 2-3mpg less. Now have 87k miles, manual transmission, tend to be heavy footed

 

All car manufacturers like to exaggerate (lie) about the fuel performance of their vehicles. Nonetheless trying to measure it by taking the actual tank fill ups and calculating it out is an enormous pain. Just use the displayed information. It is consistent enough and accurate enough for most people's purposes.

 

Is it an enormous pain?
I'm already going to fill up the gas tank. I'm going to get a receipt because I keep track of my expenditures. The receipt tells me how much gas I pumped. The trip computer, which I reset each tank, tells me how many miles I drove.
To this point, I've done nothing I wouldn't do if I wasn't tracking fuel mileage.

1) Now I use my handy ink pen kept in my center console to write the trip and cumulative mileage on the receipt. Just for kicks, I also write the fuel efficiency calculated by the car. Then I stick the receipt and my credit card back in my wallet. Total time, include cycling through the different screens, is maybe 10-15 seconds.

2) When I get home, I enter the date, cumulative and trip mileage, amount of gas pumped, and the Fit-calculated mpg into a spreadsheet I created probably a decade ago for a completely different car. The spreadsheet automagically calculates my efficiency at the pump and also calculates my total lifetime efficiency since getting the Fit. Total time to open the spreadsheet, enter the new data, and pat myself on the back is maybe 10-15 additional seconds.

I have plenty of things to do, but not so many that I can't spare 20-30 seconds every time I fill my tank to keep a decent record of my fuel efficiency. Because I write down the efficiency calculated by my Fit I can also tell you that (for my Fit) it is not consistent or accurate. Here is the delta (Fit - pump) for my past 15 tanks, where my overall average was 39.7 mpg.
0.05 mpg
4.57 mpg
0.10 mpg
-1.49 mpg
2.35 mpg
-0.36 mpg
-0.33 mpg
1.56 mpg
3.35 mpg
-2.64 mpg
3.38 mpg
-1.60 mpg
-1.74 mpg
1.66 mpg
1.54 mpg

Finally, I'm not sure if all manufacturers lie about fuel efficiency. Perhaps most drivers don't drive in a manner that maximizes fuel efficiency. I've owned something like 10 different (economy) cars over the past 25 years, and driven or rented at least 20-30 other vehicles for moving or work or travel, ranging from U-haul moving vans to full size trucks to economy cars. I've kept track of my fuel efficiency in all of them (I'm weird) and can say that I've never driven a vehicle that returned lower fuel efficiency than the manufacturer specified.

 

Fuelly website/app.

 

If you really care that much about hypermiling or your overall MPG's than you really need a better hobby. Squeezing .4 more MPG's and recording it for future reference does nothing for you. Or for anyone else.


Come on people. lol

 

What's it to you if someone does that? Is that any less valid a hobby than playing guitar or collecting old lawnmowers or dressing up little Japanese (Mexican) cars with carbon fiber trim? Hell, if all we all wanted was the ability to fit anything we could think of in our vehicles we'd be driving minivans or huge-a$$ pickups. We're here at least in part for the mileage.

Nobody should feel belittled for trying to squeeze some more miles out of the gas tank in a Fit.

 

NWCH - Not sure if you were responding to me or speaking more generally. I'm certainly not a hypermiler (e.g., I'm not going to do the pulse and glide in traffic) although I do drive for efficiency in the sense that I don't start quickly or brake hard and I don't speed.

I am a record keeper. As I said, I track my expenditures. I track fuel mileage. I track maintenance on my vehicles. Tracking fuel efficiency does serve a useful purpose for me. Most importantly, (declining) fuel mileage can provide an early indicator of some issue with your car. I know what mileage my Fit gets on long drives to visit my sister and nieces. I know what mileage it gets on more local driving. If I suddenly go from 40+ mpg on a long trip to 30 mpg, that's a good clue that something is up with my Fit. Maybe I can catch an issue before it becomes an expensive problem. So, the 20-30 second time expenditure per fill up I outlined in my previous post could save me money in the long run.

To an external observer with different tastes, the things that interest any of us can seem silly or a waste of time/money, but I figure that as long as you're not hurting anyone you're free to do what makes you happy. For example. I used to ride a BMX-style bicycle when I was a kid. Now I ride two big boy bikes. With 700c tires and cool bottle holders and even shiny red anodized valve stem caps. But I'm not going to tell you that collecting vintage BMX bikes is stupid or that you need a better hobby because that would be rude. If it makes you happy, that's wonderful. Your hobbies don't have to be of interest or useful to me, just like mine don't need to be useful to you.

 

My 2007 Honda Ruckus with 32,400 miles get 100 miles to the gallon.

 

2012 Toyota Prius (Gen 3).
January - February 2024:
Total distance driven: 8,430 miles.
Overall gas mileage: 73.6 mpg.

 

I'm a record keeper too. I created a Google form and it tracks my responses into a Google sheet so I can keep track of my gas mileage.

I embrace my dorkiness and all its glory. Tracking things has helped me become debt free at 43 years old with a paid off house and cars. Without debt, the extra funds go into investing. My investment accounts make more than my day job. My finances I tracked with a spreadsheet at first, then started using Mint, but now use monarch money.