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Getting a Proper "Miles to Empty" Reading

Discussion in 'Gen 3 Prius Fuel Economy' started by nickv84, Oct 14, 2012.

  1. nickv84

    nickv84 Junior Member

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    Hi everyone.

    I bought my 2012 Prius Two a few weeks ago and I am loving it! I have an 86 mile round-trip commute and I have done two fill-ups on my own. I calculated each tank manually and I achieved 53.5 mpg and 54 mpg, respectively.

    The thing is, the "miles to empty" indicator still puts my tank estimate at around 525 miles while my actual driving should yield me 625+. At the end of the week, I filled up with two remaining pips (estimated 100 mile range) after driving 426 miles. The car, however, only took 7.897 gallons. So I had 4 remaining gallons - clearly enough for more than 100 miles.

    Does it take away for the system to properly calibrate? Is this a known issue? It's not a big deal since I know I'm getting 50+ mpg and my fuel-ups are much cheaper but it would be nice to get an accurate reading!
     
    #1 nickv84, Oct 14, 2012
  2. bisco

    bisco cookie crumbler

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    welcome! the last two gallons are safety reserve. the low gas warning comes on after 10 gallons are gone, so i think it only uses 10 gallons for the calc.
     
    #2 bisco, Oct 14, 2012
  3. nickv84

    nickv84 Junior Member

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    Thanks for the welcome! This seems like a great forum. Appreciate the info.
     
    #3 nickv84, Oct 14, 2012
  4. bisco

    bisco cookie crumbler

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    it is great, great car, great people. enjoy!
     
    #4 bisco, Oct 14, 2012
  5. fuzzy1

    fuzzy1 Senior Member

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    All but one of my cars have had the low fuel warning light flash on, or the needle fall to 'E', 100-ish miles before one would expect from simply calculating MPG X claimed tank capacity. As already mentioned, this is for a safety reserve. It is necessary to cover human foibles and the real world's very wide short term MPG variations caused by variable weather, cold starts, mountain climbs, and bad traffic.

    Cwerdna has frequently posted a link to a Ford engineer's discussion about this and other human factors 'adjustments' that the car manufacturers build into their fuel gauges, but I don't have it handy.

    The one car I intentionally ran dry went just over 120 miles beyond its low fuel warning light. The four cars since have all gone at least 50 miles past, without going dry.

    But don't count on this, especially without testing it beforehand in a safe situation at a time of your choosing and convenience. There can be wide variations between cars, driving conditions are variable, and hills can tilt some of the fuel away from the intake. A long ago car did run dry on me just above 'E'. And Gen2 Prii with fuel tank bladders are infamous for running out early.

    [​IMG] [​IMG]
     
    #5 fuzzy1, Oct 14, 2012
  6. rebenson

    rebenson Member

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    I have found that when when you fill up "early" it seems to impact your miles to empy (fill up)...

    I know it went up when I went up to 10 Gallon fill up . Actually that is the MOST i have taken it...

    Since most cars I drove prior to Prius averaged 300 to 350 miles, a 100 more miles per fill up ( and buying less gas) is ok with me...
     
    #6 rebenson, Oct 14, 2012
  7. Codyroo

    Codyroo Senior Member

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    A more accurate estimate of your DTE (Distance To Empty) would be taking your consumption screen and multiplying it by 11. Thus, if your CONS. screen read 55 mpg, then you could go around 605 miles and be very close to running out of gas (or already have run out).

    A better estimate is to muliply your CONS. value by 10. Thus, 55 mpg would say fill up at 550 miles or earlier. You shouldn't run out of gas this way.
     
    #7 Codyroo, Oct 14, 2012
    markabele likes this.
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