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If my avg MPG is 41.7, when I fill up, why does the range only indicate 420miles?

Discussion in 'Prius v Fuel Economy' started by DougB, Apr 23, 2013.

  1. DougB

    DougB New Member

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    My 2013 Prius V tank holds 11.9 gallons. If my average mpg is 41.7, shouldn't I be getting 41.7 x 11.9=496 mile range?? Maybe someone else could comment on why the range is significantly less than what simple math would indicate. The 41.7 mpg hasn't changed for about 500 miles and I have about 8800 miles on the car. Bought it back in Dec, 2012(about 5 months worth of driving). I live in Los Angeles so about 50%/50% on city/highway driving.
     
    #1 DougB, Apr 23, 2013
  2. Sfcyclist

    Sfcyclist Senior Member

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    not sure what the car uses for reference on gallons of gas left but it's def. and estimate. I had 3 gallons of gas left yet it yet my range is only 46 miles. I'm sure it's used as reference only. Even it were more accurate you would want it to be conservative.
     
    #2 Sfcyclist, Apr 23, 2013
  3. 4everS2K

    4everS2K Junior Member

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    The range is not based on the entire tank of gas. That's why you are able to drive a lot of miles even after "Distance to empty" turns to "Zero". Basically the range is based on 10 gallons with approx. 2 gallons in reserve.
    Since it's based on 10 gallons, when you assumed you have 3 gallons left, the range was based on only 1 gallon which would get you about 46 miles based on your current 44.5 MPG.

    My other car (Infiniti G37) holds about 20 gallons (what a big tank!) and its range is based on 17 gallons with 3 gallons in reserve.
     
    #3 4everS2K, Apr 23, 2013
  4. Sfcyclist

    Sfcyclist Senior Member

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    makes sense!

    Next time I will have to drive it past "0" miles left. That mean my last tank, I could have gotten close to 500! I was at 412 with about 3 gallons left! To leave a safety margin, 88 miles with 2 gallons should be no problem!
     
    #4 Sfcyclist, Apr 23, 2013
  5. fuzzy1

    fuzzy1 Senior Member

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    The difference is a safety margin, and is roughly consistent with all (except one) of the cars that this household has ever owned, five different brands. Some safety margin is essential because fuel consumption can be very highly variable (driver, road surface, traffic conditions, weather, hills, and engine warmup cycles), fuel gauging components are cheap and imprecise, and the usable fuel level even changes with road slope (uphill vs. downhill).

    If no safety margin was built in, no bias low, then changing conditions would cause a non-negligible fraction of the cars that passed these signs with 95 miles of fuel remaining to run out of fuel before reaching the next gas station. BTW, cell phone coverage in these areas, to call AAA or Toyotacare for assistance, is spotty to nonexistent:
    [​IMG][​IMG]

    No car maker customer support hotline wants to deal with a boatload of angry customers whose cars ran dry before the 'mile to empty' said it would. So a considerable margin is usually built in.
     
    #5 fuzzy1, Apr 23, 2013
    F8L likes this.
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