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Unscientific speculation as to the oddities of the 'guess gauge'

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  • Rob Palkowski
    I ve been mulling over what might be causing the oddities of the fuel gauge in the Pirus, and the following idea occurred to me; I just wanted to see if any
    Message 1 of 6 , Jul 1, 2004
      I've been mulling over what might be causing the oddities of the fuel
      gauge in the Pirus, and the following idea occurred to me; I just
      wanted to see if any more technically-minded people out there thought
      it made any sense.

      As most of us know, the fuel tank is 'lined' by a 'bladder' that
      changes shape in order to minimize fuel fumes that might otherwise
      escape the fuel tank.

      If the fuel is measured by the level of fuel that's in the tank the
      following possibility exists:

      If the bladder is 'shrinking' as fuel is consumed along the dimensions
      of length and width more than height, the level (or height) of fuel in
      the tank will tend to stay higher than it normally would, until the
      bladder starts shrinking vertically, at which point the fuel level
      would start declining more conventionally.

      If this is the case in fact, two possible solutions suggest themselves
      to me:

      Either reconstruct the bladder to be more inclined to retain a stable
      length and width, or devise a new method of determining the amount of
      fuel in the tank. One idea that immediately comes to mind is simply
      weighing the contents of the fuel tank (or more accurately, the
      bladder), and calculating 'fullness' of the tank based on mass.

      However, I don't know if different fuels have different densities, so
      that may not be feasable.

      Just something I was pondering.

      --
      Rob
    • bobjbkln
      «Either reconstruct the bladder to be more inclined to retain a stable length and width» The whole purpose of the bladder is to shrink. This limits the
      Message 2 of 6 , Jul 1, 2004
        «Either reconstruct the bladder to be more inclined to retain a stable
        length and width» The whole purpose of the bladder is to shrink.
        This limits the amount of air in the tank, limiting the amount of gas
        that evaporates into (and pollutes) the atmosphere. The non linear
        (slower decline when full) change in the gauge is programmed in and
        is similar to other vehicles' gauges, even those that are analog.
        The lack of consistency from tank to tank, however, seems to be more
        pronounced in the Prius than other cans. But I think that it is not
        much different in the European models that do not have the bladder,
        although I could be wrong here.
        --
        Peace,
        BobJ


        --- In toyota-prius@yahoogroups.com, Rob Palkowski <ghoti@s...> wrote:
        > I've been mulling over what might be causing the oddities of the
        fuel
        > gauge in the Pirus, and the following idea occurred to me; I just
        > wanted to see if any more technically-minded people out there
        thought
        > it made any sense.
        >
        > As most of us know, the fuel tank is 'lined' by a 'bladder' that
        > changes shape in order to minimize fuel fumes that might otherwise
        > escape the fuel tank.
        >
        > If the fuel is measured by the level of fuel that's in the tank the
        > following possibility exists:
        >
        > If the bladder is 'shrinking' as fuel is consumed along the
        dimensions
        > of length and width more than height, the level (or height) of fuel
        in
        > the tank will tend to stay higher than it normally would, until the
        > bladder starts shrinking vertically, at which point the fuel level
        > would start declining more conventionally.
        >
        > If this is the case in fact, two possible solutions suggest
        themselves
        > to me:
        >
        > Either reconstruct the bladder to be more inclined to retain a
        stable
        > length and width, or devise a new method of determining the amount
        of
        > fuel in the tank. One idea that immediately comes to mind is
        simply
        > weighing the contents of the fuel tank (or more accurately, the
        > bladder), and calculating 'fullness' of the tank based on mass.
        >
        > However, I don't know if different fuels have different densities,
        so
        > that may not be feasable.
        >
        > Just something I was pondering.
        >
        > --
        > Rob
      • Rob Palkowski
        ... I wasn t suggesting not to have the bladder shrink at all, but rather to have it shrink the vertical dimension first, so that the level of the fuel in the
        Message 3 of 6 , Jul 1, 2004
          On 01 Jul 2004, at 14:22, bobjbkln wrote:

          > «Either reconstruct the bladder to be more inclined to retain a stable
          > length and width» The whole purpose of the bladder is to shrink.
          > This limits the amount of air in the tank, limiting the amount of gas
          > that evaporates into (and pollutes) the atmosphere.

          I wasn't suggesting not to have the bladder shrink at all, but rather
          to have it shrink the vertical dimension first, so that the level of
          the fuel in the tank will actually go down.

          This, again, from the assumption that the fuel gauge is getting a
          reading from the height of the liquid in the tank.

          --
          Rob
        • Donald Canales
          One idea that immediately comes to mind is simply weighing the contents of the fuel tank (or more accurately, the bladder), and calculating fullness of the
          Message 4 of 6 , Jul 1, 2004
            One idea that immediately comes to mind is simply
            weighing the contents of the fuel tank (or more accurately, the
            bladder), and calculating 'fullness' of the tank based on mass.

            However, I don't know if different fuels have different densities, so
            that may not be feasable.

            _______________

            I like the idea of weighing the fuel. It could be weighed every time the vehicle is powered up and the display set accordingly. As the car uses gas this can be subtracted from the display.

            As far as the density, it can't be that different. It certainly would be better than what we already have.

            I know if you are near empty and you put only 2 or 3 gallons in, it won't register the extra fuel. What it you put in 5 or 6 gallons? Will it show full? If it was weighed, at whatever density, it must be more accurate.





            [Non-text portions of this message have been removed]
          • bobjbkln
            Meant for the group, I presume: I think there are several things going on here: 1. There s the temperature. No question that cold weather reduces the capacity
            Message 5 of 6 , Jul 2, 2004
              Meant for the group, I presume:

              I think there are several things going on here:

              1. There's the temperature. No question that cold weather reduces the
              capacity by about a gallon.

              2. Because Toyota has set the flash point so high, the amount of miles
              will vary depending upon where/how you are driving.

              3. I'm pretty sure that some folks don't notice when the flash point
              is
              first reached. Perhaps the Nav Lady should make an announcement. (I
              believe that this accounts for the few who only get 30 miles after the
              flash and then run out).

              4. The tank is too small for that size of car. My take on this is that
              Toyota uses the exact same bladder and tank that they used in the
              Classic.
              This is an obvious economy measure, but one that has caused a lot of
              headaches for them. The only change that was made was the value of the
              flash point. Some Classic owners have complained that they ran out of
              gas
              two miles after the flash point. I've never had this happen in my 2001
              Classic, but then I treat it like a normal car and fill up when there
              are
              a couple of bars left.

              Jerry


              --
              Jerry Jorgenson
              jerry@...
              http://www.j3iss.com/





              --- In toyota-prius@yahoogroups.com, "bobjbkln" <bobjbkln@h...> wrote:
              > «Either reconstruct the bladder to be more inclined to retain a
              stable
              > length and width» The whole purpose of the bladder is to shrink.
              > This limits the amount of air in the tank, limiting the amount of
              gas
              > that evaporates into (and pollutes) the atmosphere. The non linear
              > (slower decline when full) change in the gauge is programmed in and
              > is similar to other vehicles' gauges, even those that are analog.
              > The lack of consistency from tank to tank, however, seems to be
              more
              > pronounced in the Prius than other cans. But I think that it is
              not
              > much different in the European models that do not have the bladder,
              > although I could be wrong here.
              > --
              > Peace,
              > BobJ
              >
              >
              > --- In toyota-prius@yahoogroups.com, Rob Palkowski <ghoti@s...>
              wrote:
              > > I've been mulling over what might be causing the oddities of the
              > fuel
              > > gauge in the Pirus, and the following idea occurred to me; I just
              > > wanted to see if any more technically-minded people out there
              > thought
              > > it made any sense.
              > >
              > > As most of us know, the fuel tank is 'lined' by a 'bladder' that
              > > changes shape in order to minimize fuel fumes that might
              otherwise
              > > escape the fuel tank.
              > >
              > > If the fuel is measured by the level of fuel that's in the tank
              the
              > > following possibility exists:
              > >
              > > If the bladder is 'shrinking' as fuel is consumed along the
              > dimensions
              > > of length and width more than height, the level (or height) of
              fuel
              > in
              > > the tank will tend to stay higher than it normally would, until
              the
              > > bladder starts shrinking vertically, at which point the fuel
              level
              > > would start declining more conventionally.
              > >
              > > If this is the case in fact, two possible solutions suggest
              > themselves
              > > to me:
              > >
              > > Either reconstruct the bladder to be more inclined to retain a
              > stable
              > > length and width, or devise a new method of determining the
              amount
              > of
              > > fuel in the tank. One idea that immediately comes to mind is
              > simply
              > > weighing the contents of the fuel tank (or more accurately, the
              > > bladder), and calculating 'fullness' of the tank based on mass.
              > >
              > > However, I don't know if different fuels have different
              densities,
              > so
              > > that may not be feasable.
              > >
              > > Just something I was pondering.
              > >
              > > --
              > > Rob
            • jjust_jay
              ... I don t think the tank is too small for the car. This is the first car I ve owned where I could consistently drive over 400 miles without refueling.
              Message 6 of 6 , Jul 4, 2004
                --- In toyota-prius@yahoogroups.com, "bobjbkln" <bobjbkln@h...> wrote:

                > 4. The tank is too small for that size of car. My take on this is that
                > Toyota uses the exact same bladder and tank that they used in the
                > Classic.
                > This is an obvious economy measure, but one that has caused a lot of
                > headaches for them.

                I don't think the tank is too small for the car. This is the first
                car I've owned where I could consistently drive over 400 miles without
                refueling. Typically you'll see a range of somewhere under 300 miles
                per tank on most cars.
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