mpg calculated vs computer

Discussion in 'Prius v Fuel Economy' started by alfon, Nov 4, 2011.

  1. crpriusv

    crpriusv Junior Member

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    Yup. After 3 fuel-ups, my v's computer numbers are averaging about 3% higher than calculated mpg's when filling to the first click.
     
  2. RD_CDN_newbie

    RD_CDN_newbie New Member

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    After traveling 1993 km I am noticing a difference of 3 to 5.5% from what computer reports versus calculated.

    Example trip states 4.9 L/100km (48 MPG) Actual calculated 5.186L/100km (45.37 MPG). I took possession of the car at 149 km and average fuel consumption from beginning of owning is 5.304L/100km (44.35 MPG) calculated versus odometer of 5.1L /100 km (46.12 MPG).

    I am very happy as my old Taurus was averaging 11 - 13 L/100km (11.8 during summer). Also as I chose more efficient routes and improve technique I am sure fuel economy will get better.
     
  3. vlady

    vlady Junior Member

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    My last fill up was opposite.
    Went to the station (the same one) with 437.8 on trip meter 45.3 mpg, one bar on fuel meter and orange light. Pump clicked off at 9.45 gallons.
    So my manual calculation came out as 46.3. I used to get 2-3 mpg lower on hand calc with trip range between 440-470 and 10-10.5 gallon fill ups.
    I do not thing that pump shut off prematurely, fuel meter came out full-all bars.
     
  4. alfon

    alfon Senior Member

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    Trip A - 8,617.5 miles / indicated mpg's - 56.1 / calculated 53.54 / avg. indicated mph 40 /
    gals' used: 160.955 / diff. 2.56 mpg
    Gas is reg with 10% Ethanol
    Tires for the last 500 miles / Bridgestone ep422 Ecopia (44 psi in all four tires) / 195x65x15 (before that Michelin Energy Saver AS) / with 44 psi in all four tires.

    Here is a the result with well over 8,000 miles on trip A without
    resetting in our 2010 Prius.
     
  5. CharlesJ

    CharlesJ Member

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    I buy this but how much does the gas expand? And, if one is on a trip and gets right back on the road you'd use enough, I would say before the temperature makes much difference in volume, no?
     
  6. CaptainPlanet

    CaptainPlanet New Member

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    My yesterday's reading of the computer was way off. It calculated 54 mpg while fuelly said 64 mpg! But today both the V Computer & fuelly were spot on.
     
  7. msirach

    msirach Member

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    We have 80,000 miles on our 2010 and it has been filled to the top many times. It has never thrown a code or had any issue.
     
  8. vlady

    vlady Junior Member

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    Just a follow-up on my strange fill up. I turned out as a worst mpg. Computed stated 46, manual came out 39 (have not gotten this number even during winter ). Next fill up was back to normal - 2-2,5 mpg difference between computer/hand calc.
    The only thing comes to mind is hot weather. Otherwise I have no other explanations
     
  9. rich s

    rich s Blackie II The Prius

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    Usually about 2 Mpg less then the display shows....Rich
     
  10. crpriusv

    crpriusv Junior Member

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    And now after 12 fuelups my Fuelly calculated lifetime average for 5100 miles is 44.5 mpg vs the computer's displayed lifetime average of 45.9 mpg. This is consistent with my earlier posting, with the computer's mpg still reading about 3% greater than the calculated mpg.
     
  11. rich s

    rich s Blackie II The Prius

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    My milage always runs displayed 2.1-3 more miles then the calculated does. 53.3 is usually 51 ....51 is 49. This is a standard. Question is WHY? Why does Toyota let this happen? They seem to be up on everything else. Why is this displayed wrong? I see everyone telling their 2-4% off, but not the reason .... Thanks .....Rich. I have a 2012 II Hatchback
     
  12. User37

    User37 Can spell PRIUS

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    I think making the onboard display a bit optimistic is not a Toyota special, but it is a generic trend in the industry.

    The reason? Probably to compliment the owner. Here we are on a forum for fuel efficient car, so this subject will come up very often. But out there on the road, the majority of owners won't spend the time to calculate the true MPG. They see the car reporting a number and they'll go with it.
    I don't think it is a bad intention of the manufacturer. It is more like presenting the car in a good light.
     
  13. xs650

    xs650 Senior Member

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    Not all manufacturers do that. My wife's Acura TL is pretty much spot on, my Corvette reads 1% low.
    A lie isn't a good intention.
     
  14. User37

    User37 Can spell PRIUS

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    Where would you draw the line between "lying" and "not very accurate" 1% is ok, but 2 - 4% is not good? ;)

    Just do a google search on "MPG accuracy", there are about 10 million hits. Some cars report more accurate numbers some do less, but all err on the side of the manufacturer.
     
  15. xs650

    xs650 Senior Member

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    1% is a low enough error to be considered reasonable for an honest attempt.. Gas station pump accuracy is only required to be about 1/2% so 1% from a car computer is good.

    If you look back through older posts, you will discover that the Prius computer MPG numbers average about 6% optimistic +/- about 1%. That is a lie.
     
  16. vlady

    vlady Junior Member

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    I do not feel being lied - I'm still 2-3 mpg over advertised 42 combined mpg (44/40). Yes , there is a problem with calibration of the equipment . I recall that during winter the difference was very little, became more noticeable during summer gas blend.
     
  17. fafield

    fafield New Member

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    My Prius v now has about 6500 miles on it. Over the last 2500 miles, the car's computer says I got 46.0 MPG. The actual economy was 43.6 MPG, a 5.5% error. Seems that Toyota has the " feel good" approach to its fuel economy gauge. My wife's Acura MDX is always spot on accurate. After 20 years of Honda products, this is my first Toyota. While I'm happy with 43.6, I'm not happy that Toyota seems fine with an error this large, judging by the reaction I got from my dealer and reports from numerous others on this site.
     
  18. deegowd

    deegowd New Member

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    I never wait for the pump to 'click' and always stop fueling at 10 gallons (a practice I picked up before buying my Prius v). So far, I have fueled up 17 times that way and 7 gallons once, so I know that my car has consumed almost exactly 177 gallons over it's lifetime. The ODO shows 8674 miles to date and there is about a gallon and half of gas left in the tank (that's about 49.4 MPG). The computer milage for the car shows 52.1, which is a difference of about 2.8 MPG or 5%.
     
  19. skwcrj

    skwcrj Member

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    From my fuel records over the last 11 months (almost 11k miles), the average difference between the indicated and actual mpg has been 5%.
     
  20. Vinoh

    Vinoh Junior Member

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    I finally got around to hooking up an OBDII device to my 5 ATP. Very interesting that the reported speed in DashCommand on my iPad was about 2 MPH lower than the number on my car's display. I had noticed that this was true for the car's display vs. radar signs on the road, but I didn't expect the OBDII data to be different. I guess Toyota is purposely misreporting the speed on the display, maybe in an attempt to slow us down.

    I suspect this relates to our discussion of the fuel efficiency error. If the speed (probably the odometer reading) is too high, then the reported mpg might be too high as well as a result.
     
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