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Odd fuel gauge behavior

Discussion in 'Gen 3 Prius Fuel Economy' started by lamontcranston, Nov 9, 2009.

  1. lamontcranston

    lamontcranston Umbra Tenet

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    Here's the skinny:

    -Driving home with about 140 miles since fill-up. MFD says about 63mpg, so assuming the normal error, I've used a little over 2 gallons.

    -Fuel gauge shows full minus one pip. I would have expected full minus two at this point.

    -Then, after a run that was neither strongly uphill nor strongly downhill, the fuel gauge goes up to completely full for about ten minutes.

    -Then, it goes down to full minus one for about ten minutes, then full minus two.

    -When I got in it this morning it showed full minus three, then after about ten minutes went to full minus two. I drove another 50 miles and it is still at full minus two.

    -Distance-to-empty seems to stay consistent through this period.

    So, does anyone have an idea? This may be my first tank on "winter blend"... is there a possibility of foaming or something? I don't know if the Prius gas gauge is fed by a float like older car tanks, or is measured by weight, or what.

    Should I be worried if this behavior continues? Has anyone else seen this?
     
    #1 lamontcranston, Nov 9, 2009
  2. qbee42

    qbee42 My other car is a boat

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    The Prius uses a float like most cars. There is also a damping time constant to reduce rapid swinging of the fuel gauge, and also an inclinometer to compensate for grade. I suspect your fuel was sloshing around a bit as you went up and down hill. The distance to empty calculation, on the other hand, is working from calculated remaining fuel.

    Tom
     
    #2 qbee42, Nov 9, 2009
  3. fuzzy1

    fuzzy1 Senior Member

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    Nothing odd here. Not only does this behavior happen in my Prius, its analog equivalents happened to the gas gauge needle in every previous car I've had.
     
    #3 fuzzy1, Nov 9, 2009
  4. a64pilot

    a64pilot Active Member

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    It's simply just not as accurate a device as you want it to be.
     
    #4 a64pilot, Nov 9, 2009
  5. lamontcranston

    lamontcranston Umbra Tenet

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    I'd say that's the answer I needed. I'm surprised, I guess, with all the other technological wizardry that they're using an old-school float to do the initial measurement. Oh well, whatever works.
     
    #5 lamontcranston, Nov 9, 2009
  6. a64pilot

    a64pilot Active Member

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    To add to the insult, most vehicles are intentionally mis-calibrated so that about 75% of the fuel has been used when the gauge reads half full.
     
    #6 a64pilot, Nov 9, 2009
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