calculated vs. computer MPG - Please post your results

Discussion in 'Gen 3 Prius Fuel Economy' started by F8L, Jul 10, 2009.

  1. pakitt

    pakitt Senior Member

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    Average error in fuel consumption is, world-wide, 5-7%.
    The miles-to-travel-to refuel, at least for me, it goes to 0km, about 10mi/20km after it starts beeping. The problem is that in the tank I still have around 10L/about 2 gallons (?), that with a Prius are on average at least worth about 200km/120mi.
    So I don't understand how you managed to end up "dry" after the indicator went to 0mi.
    I mean, how much did you drive after the beep and the indicator of the "miles left to tank" went to 0? 100+ miles?
     
  2. WIChris

    WIChris Junior Member

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    The story's too long to repeat in detail, but I was driving on a highway (so getting lower mpg to begin with--about 44 on a very cold night in a new car), didn't get any beeping/warning when the fuel gauge bottomed out, drove several miles and had more miles to go than I was comfortable with before I could re-fuel, so dropped my speed down pretty low and economized for about 12 more miles. It's possible I could have gone farther, but in a new car (this was only my 3rd fill-up) and well outside my home-town, I didn't want to take chances.
    By the way, my calculated MPG has been 5% off thus far.
     
  3. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Dang it, no:

    Honda Civic Hybrid for example, typically underestimates actual mileage, though it's pretty close. If it says 5.0 liters/100 km, reality is likely 4.9, maybe even 4.8.

    Our Prius is averaging 6.4% error, in favour of the house :rolleyes:, over the past year I've tracked it.
     
  4. rainmaster

    rainmaster Junior Member

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    First tank on brand new 2011 Prius 2 was 430 miles on 9.41 gals of fuel for 45.696 MPG's. Computer said 48.1 MPG. So par for the course. This with temps in 40-50's and tires inflated as per dealer (35 and 33) and no effort to save gas in a commute that is 80 miles each way with 55 of those miles at highway speeds (65-75mph). Could not be happier with these results.
     
  5. Lemooron

    Lemooron Junior Member

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    I have had my 2011 Three for just about 4 weeks. It seems like the more miles you drive between fill ups the higher the mpg is and the difference between the dash reading and the calculated is closer. Here is my data.

    Miles Traveled /Gallons /EST MPG/ Actual MPG /Difference
    254.9/ 5.288/ 50.4/ 48.20/ 2.20
    66.9 /1.573/ 46.9/ 42.53/ 4.37
    189.1/ 4.047/ 49.7/ 46.73 /2.97
    269.1/ 5.127/ 54.7/ 52.49 /2.21
     
  6. Southern Dad

    Southern Dad Active Member

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    My Prius has only one fill up so far. I log my fill ups in Fuelly. The NOTES field I'm using for logging the mpg showed on my display. The first fill up was 49.5 mpg even though the display showed 52.3 mpg.

    I have a pretty long commute each day. Next week, I will fill my Prius every day at the same station, using the same pump, facing the same direction. Just for an experiment. Click on my Fuelly if you want to watch and see the comparison of calculated vs computer mpg.
     
  7. charlie_rivera1

    charlie_rivera1 Junior Member

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    I'm tracking my mileage on my new 2011 Prius IV using both methods; Cumputer and Manual. I have an account with Fueleconomy.org and it calculates the mileage based on the fill ups and odometer. I have had about 12 fill ups and the computer has always been between 3 - 4 MPGs higher than the actual reading I'm getting by the miles driven in a tank. I have filled up my car on multiple gas pumps and it has always given me this difference.

    I'm right now averaging 53.6 mpg (calculated) vs 57.1 (computer)


     
  8. Southern Dad

    Southern Dad Active Member

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    I've filled up my tank three times.

    Column 1 Column 2 Column 3 Column 4 Column 5 Column 6
    0 Fill Up Miles Gas Added Actual Shown Difference
    1 Fill Up 1 454 miles 9.17 gallons 49.5 mpg 52.3 mpg 5.3%
    2 Fill Up 2 277 miles 5.39 gallons 51.4 mpg 54.6 mpg 5.8%
    3 Fill Up 3 303 miles 6.23 gallons 48.7 mpg 51.7 mpg 5.8%


    So far, I'd say my offset is 5.3 to 5.8 percent.
     
  9. alfon

    alfon Senior Member

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    Lets hope that Toyota does right by engineering the
    MPG guage to read accurately in 2012 and above models.

    It is my opinion that Toyota intentionaly made the guage
    read more mpg than it should of.

    Every Toyota Prius 2010 and above has the same error rate,
    no coincidence in my book.

    It would be nice if Toyota could do an upgrade software to
    make the guage accurate.

    If it could be proven that Toyota intentionally engineered the
    mpg gauge to read higher to mislead owners there should be legal action, class action suit, against them.

    al
     
  10. cycledrum

    cycledrum PSOCSOASP

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    I've had 3 fillups and I'm seeing about 5% error with CONS gage being optimistic.

    CONS gage , Actual , % error

    55.2 , 52.8 , 4.3%
    49.5 , 46.9 , 5.3%
    52.5 , 49.6 , 5.5%

    -------------

    So, I can count on actual being almost 3 MPG less than gage.
    This is quite a bit more error than the 2009 Prius which was maybe 1/2 that error or less.

    All those times renting the car for a day, I'd see #'s like 55 MPG, but was never able to get accurate actual #'s driving less than 200 miles.

    Little bit disappointing, but not horrible. It's still doing well given the time of year and average MPH's of low 20's MPH, lot of city driving and shorter trips of under 5 miles.
     
  11. kgall

    kgall Active Member

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    The following are not completely comparable, since my trip B odometer has not been reset since the car was made, but I did not get the car till it had 210 miles on it, but there shouldn't be too much distortion.
    Over 42737 miles, the computer says 49.4 mpg.
    Over 42527 miles, my calculations say I average just under 47.0.
    I think the car was built Sept. 09.
     
  12. Scott196250

    Scott196250 ScottnATL

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    I just purchased a used 2010 Prius II with 45K on the Oh-Doh, and my first fill-up after 405 miles was 8.886 gallons (45.6 mpg). Trip A computed an mpg of 47.2. I dont know all the tricks to hypermileing yet, but I had Eco Mode on the entire time and I did not drive aggressively whatsoever. I am a tad disappointed that I am not one of the lucky ones to own a 55+ mpg Prius, but maybe the summer fuel mix and warmer temperatures will yield a better result in six months. Of course, one fill up is not a large sample size . . . I will continue to post results and see what occurs over time.
     
  13. ryano7700

    ryano7700 Junior Member

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    Through 9 fill-ups--Calculated is 45.5 mpg. Weighting the MFD average based on the mileage for each tank is 48.0. This matches my trip B that has not been reset. The difference of 2.5 appears to be consistent with everyone else. Prius manufactured 8/11.
     
  14. Scott196250

    Scott196250 ScottnATL

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    Two fill-ups and I have pumped in 18.062 gallons over 867.0 miles = 48.00 mpg; the computer calculates 50.0 mpg. On my next post I will record the month and year my 2010 Prius was manufactured. This differential is entirely consistent with what many have posted here; thanks so much.
     
  15. San_Carlos_Jeff

    San_Carlos_Jeff Active Member

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    Vehicle:
    2012 Chevy Volt
    Model:
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    Miles: 91,576
    Gallons used: 2043.08
    Calculated lifetime MPG: 44.8
    Indicated lifetime MPG: 46.0
    High tank (indicated): 54.1
    Low tank (indicated): 41.7
    Best range: 483 miles
     
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  16. NargilFenris

    NargilFenris Junior Member

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    Last three fill ups the computer has over estimated my MPG by 3. Mine is a 2011 model, will have to check for the month.
     
  17. alfon

    alfon Senior Member

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    Like yours, ours has been off by 3 mpg since new, and we now have over 66,000 miles and it has not improved.

    al
     
  18. Old Bald Guy

    Old Bald Guy Old Bald Guy

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    When I bought my 2010 Gen III V, 17" wheels, navigation, heated leather butt warmers, and more ... I noticed that my calculated MPG was about 2.25 LOWER than what the computer said.

    As the miles have piled up, the difference increased. I now have 67,000 miles on the odometer and the MPG difference is increasing. I filled up today and the computer said 47 MPG but calculated was 43.7 MPG. (driving with the butt warmers and the heater on with outside temperature of 45 or less sucks the gas). That's over 3 MPG difference.

    Manufacture date of April 2009.
     
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  19. ataylorracing

    ataylorracing ataylorracing

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    I never checked the first tanks full, but on the second the dash said my wife got 48.3 (way better than her first fill showing 42.0....but the calculator showed a reaal mpg of 45.144, 7% off. She drove 450.5 miles and put in 9,979 gallons at $35.91 total. We also put the pump on the middle speed setting if there are three on it or the slowest if only 2 clicks on it. When it clicks off we do NOT squeeze in any more at all...its done.

    12.17 at 117 mph and still getting 33 mpg at 55-60 mph!
     

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  20. Scott196250

    Scott196250 ScottnATL

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    Location:
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    Vehicle:
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    MIles driven since January 1st: 1,343.
    Gallons purchased: 27.35
    MPG actual: 49.10
    MPG computer: 51.10
     
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