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

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• 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

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
• «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
>
> 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
• ... 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
• 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]
• 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

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
• ... 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