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MPG OverEstimate on the MFD?

Discussion in 'Prius c Fuel Economy' started by HeavyUser, Mar 31, 2015.

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  1. HeavyUser

    HeavyUser Junior Member

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    Hey Guys,

    I'm on my second fill up since I purchased this awesome piece of gas saving technology. My first tank said I was getting 48mpg on the MFD but fuelly calculated 46.32, my second tank said I got 50mpg on the MFD but fuelly calculated 47.97. Is this normal for there to be such a big difference in mpg between the two, do you guys have the same results with the MFD overestimating mpg?

    On a side note, a day ago I noticed my MPG was stuck at 100mpg on the energy monitor even though the car was at a complete stop. I had to restart the system to get it functioning again, do you think this could be a bug in the system? I called the dealership about it and they want me to take it in.

    A link to my fuelly:
    SippnOnsomeGassurp (Toyota Prius C) | Fuelly
     
    #1 HeavyUser, Mar 31, 2015
  2. bisco

    bisco cookie crumbler

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    yup. on the first question. not sure about the second. my gauge goes to zero when i stop.
     
    #2 bisco, Mar 31, 2015
  3. HeavyUser

    HeavyUser Junior Member

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    Oh hey Bisco, by the way that fan noise I was hearing turned out to be a bad bearing in the fan motor. The dealership replaced the radiator fan assembly.

    I did some research on the MPG getting stuck at 100mpg, found this:

    Prior reports on various Prius boards have noted other Classic Prius' Newarkitis symptoms: no charge on the battery icon, no arrow flows on the Energy Monitor, a "stuck" Consumption screen showing many consecutive 100MPG (or 0 l/100km) segments even with the engine running at idle... It will occur randomly at first, but will get progressively worse. It's only covered for the basic 3 year/36,000 mile warranty, so be careful if you're going past on mileage as it could be very expensive... Car is fully driveable, but it's mostly an annoyance. A reboot may temporarily fix the problem. Problem has been reported on US, Canadian, and Australian Prius so far that I've noted, I don't recall one way or the other on the European/UK lists.

    Just my luck, lol.
     
    #3 HeavyUser, Mar 31, 2015
  4. bisco

    bisco cookie crumbler

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    wow, that's crazy. two defects on a fairly new car? and odd ones at that!
     
    #4 bisco, Mar 31, 2015
  5. HeavyUser

    HeavyUser Junior Member

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    Bought it brand new, 34miles on it.
     
    #5 HeavyUser, Mar 31, 2015
  6. fuzzy1

    fuzzy1 Senior Member

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    While I can't speak to the 'c' specifically, this overestimate is normal for GenIII Liftbacks. I know of no reason why the 'c' would necessarily be different.

    The GenIIs were generally closer to reality.
     
    #6 fuzzy1, Mar 31, 2015
  7. HeavyUser

    HeavyUser Junior Member

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    Have you guys noticed that even when using gas/electric(energy monitor will show gas and electric being used) the energy monitor will show 100mpg at times or could this be unique to my situation?
     
    #7 HeavyUser, Mar 31, 2015
  8. fuzzy1

    fuzzy1 Senior Member

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    No, not in my Liftback.

    But we don't drive a 'c'. This part of the display is sufficiently different from the Liftback that I wouldn't draw definitive conclusions across model lines.
     
    #8 fuzzy1, Apr 1, 2015
  9. Mendel Leisk

    Mendel Leisk Senior Member

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    I'd read the c's and v's mpg display was at least CLOSER to reality, only about 3~4% off (guess which way :rolleyes:). Our 3rd gen hatchback's off by 7.5%, over 50,000 kms calculated.
     
    #9 Mendel Leisk, Apr 1, 2015
  10. minkus

    minkus Active Member

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    An mpg overestimate of 1.5-2.5 mpg (~4% at 50 mpg) seems about normal. That's what I get, and many have reported similar. SO's '12 Hyundai Accent hatchback overestimates by about 2-4 mpg (7.5% at 40 mpg).
     
    #10 minkus, Apr 2, 2015
  11. HeavyUser

    HeavyUser Junior Member

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    Good to know, thanks gents.
     
    #11 HeavyUser, Apr 2, 2015
  12. Sean Nelson

    Sean Nelson Active Member

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    Doesn't it show 100mpg when you start off in electric mode and the gas engine hasn't come on yet? Technically in that situation it's "infinite miles per gallon", but I believe they limit the display to a maximum of 100.

    I'm in Canada, and when I start out it shows "0.0 l/100km" (litres per 100km, the way fuel economy is measured here) until the gas engine comes on and some fuel is actually consumed.
     
    #12 Sean Nelson, Apr 3, 2015
  13. HeavyUser

    HeavyUser Junior Member

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    In this picture I'm on a pretty flat road using the GAS engine and the ELECTRIC yet somehow it says 100mpg, it stays like this for some time unless give it more gas
    20150403_082943.jpg
     
    #13 HeavyUser, Apr 3, 2015
  14. bisco

    bisco cookie crumbler

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    it's probably spinning the ice without using gas. keep in mind, there's a 3 second delay between reality, and what you see on the screen.
     
    #14 bisco, Apr 3, 2015
  15. HeavyUser

    HeavyUser Junior Member

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    I figured there was a delay yet when I switch the energy monitor over after a few minutes of the 100mpg it still show the gas/electric being used. I'll take a video later on in the week.
     
    #15 HeavyUser, Apr 3, 2015
  16. bisco

    bisco cookie crumbler

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    you need an obd reader for instantaneous mpg.
     
    #16 bisco, Apr 3, 2015
  17. HeavyUser

    HeavyUser Junior Member

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    Would something like this work?

    Edit: NVM it wont let me link something to amazon. It's a bluetooth OBD reader
     
    #17 HeavyUser, Apr 3, 2015
  18. bisco

    bisco cookie crumbler

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    i don't know. maybe someone else will. i know scan gauge works, and some phone apps. i don't have one.
     
    #18 bisco, Apr 3, 2015
  19. Mendel Leisk

    Mendel Leisk Senior Member

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    ScanGauge will also report no gas usage, with engine turning over. The engine HAS to run, above some speed. On 3rd gen hatch it's around 74 kmh it kicks in.
     
    #19 Mendel Leisk, Apr 3, 2015
  20. spyderx

    spyderx Member

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    52.7 MPG actual vs. 55 MPG MDF.., I was hoping it would match
     
    #20 spyderx, Apr 3, 2015
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