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Gas tank meter

T

Tanty

Jan 1, 1970
0
My gas tank meter is so off that i can get 60 miles after I've reached the
low fuel indicator. I wanna build a more accurate one that doesn't depend on
a float.
any ideas? maybe the conductivity of petrol can be used?
 
R

RP Henry

Jan 1, 1970
0
Tanty said:
My gas tank meter is so off that i can get 60 miles after I've reached the
low fuel indicator.

And this is a problem?
 
J

John Hall

Jan 1, 1970
0
My gas tank meter is so off that i can get 60 miles after I've reached the
low fuel indicator. I wanna build a more accurate one that doesn't depend on
a float.
any ideas? maybe the conductivity of petrol can be used?

There are probably regulations about what you can do in a gas tank. If
there aren't, there should be, IMHO.
 
M

Michael

Jan 1, 1970
0
My gas tank meter is so off that i can get 60 miles after I've reached
the low fuel indicator. I wanna build a more accurate one that doesn't
depend on a float.
any ideas? maybe the conductivity of petrol can be used?

That's how its supposed to be. I heard there was actual regulation saying
that once the empty light goes on - you should have 2 - 3 gallons of fuel
left. Don't know if that is true - but that's what I've heard. In my '98
subaru legacy that is true.
 
K

Kevin McMurtrie

Jan 1, 1970
0
Tanty said:
My gas tank meter is so off that i can get 60 miles after I've reached the
low fuel indicator. I wanna build a more accurate one that doesn't depend on
a float.
any ideas? maybe the conductivity of petrol can be used?

Like Jim Thompson said, it's a thermistor. If you don't like where it
is, pull the fuel assembly out of your gas tank and bend steel wire
holding it. There's an access panel under the rear seat if you're lucky.
 
J

Jim Thompson

Jan 1, 1970
0
That's how its supposed to be. I heard there was actual regulation saying
that once the empty light goes on - you should have 2 - 3 gallons of fuel
left. Don't know if that is true - but that's what I've heard. In my '98
subaru legacy that is true.

I don't know if there's an actual regulation, but every car I've ever
owned seems to have at least 50 miles of range left after it says "Low
Fuel".

But my Frontier PU announces "Low Fuel" before the E-mark. I've never
driven it past the E-mark to test it out though ;-)

...Jim Thompson
 
R

RP Henry

Jan 1, 1970
0
I don't know if there's an actual regulation, but every car I've ever
owned seems to have at least 50 miles of range left after it says "Low
Fuel".

But my Frontier PU announces "Low Fuel" before the E-mark. I've never
driven it past the E-mark to test it out though ;-)

My first car didn't have a fuel gage, but it did have a reserve lever that
you were supposed to push back up when you refueled. Ran out once because I
forgot.

My next car had a sticky fuel gage, that would occasionally indicate 1/4
tank forever, or at least until it was refilled past the 1/4 level. Ran
that one out once, too.

The solution to both was a grease pencil on a string where I wrote the
mileage of the last fillup on the speedo glass. I now use the trip-odometer
for similar purpose.
 
J

Jim Thompson

Jan 1, 1970
0
My first car didn't have a fuel gage, but it did have a reserve lever that
you were supposed to push back up when you refueled. Ran out once because I
forgot.

My next car had a sticky fuel gage, that would occasionally indicate 1/4
tank forever, or at least until it was refilled past the 1/4 level. Ran
that one out once, too.

The solution to both was a grease pencil on a string where I wrote the
mileage of the last fillup on the speedo glass. I now use the trip-odometer
for similar purpose.

I keep a spreadsheet that calculates short and long MPG averages.
Allows me to spot plug maintenance problems, etc., well before a real
problem develops.

...Jim Thompson
 
K

Ken Taylor

Jan 1, 1970
0
Jim Thompson said:
I don't know if there's an actual regulation, but every car I've ever
owned seems to have at least 50 miles of range left after it says "Low
Fuel".

But my Frontier PU announces "Low Fuel" before the E-mark. I've never
driven it past the E-mark to test it out though ;-)

...Jim Thompson
--
An earlier car I had had a meter as a fuel gauge, seemed quite linear.
However the dash circuit board was full of dry joints and was replaced under
warranty with the next model up, complete with digital readouts. Cool!
Except that now the fuel gauge took ages to go from full to one bar off
full, but the bottom half of the gauge took no time at all! Why the hell
couldn't they linearise it??

Anyway, that leads to the methodology for the OP - use the existing legal,
safe (!) sensor and put an A/D and bar-graph display on it. All in a PIC if
you want to be clever.

Ken
 
R

RP Henry

Jan 1, 1970
0
Jim Thompson said:
I keep a spreadsheet that calculates short and long MPG averages.
Allows me to spot plug maintenance problems, etc., well before a real
problem develops.

I know that in my typical daily driving, my 91 Jeep gets about 80 miles per
quarter tank, and the 96 Toyota pickup about 90. Tank sizes are different,
but they both work out to around 18 mpg. I do a running estimate based on
fuel gage vs. odometer, and a calculation of latest mpg in my head upon
leaving the gas station.

Long trips are nice: freeway miles are about 22-24 mpg.

Now I have to fight the $60 violation notice I got in the mail because my
transponder wasn't working on the toll road.
 
T

Tom Bruhns

Jan 1, 1970
0
Tanty said:
My gas tank meter is so off that i can get 60 miles after I've reached the
low fuel indicator. I wanna build a more accurate one that doesn't depend on
a float.
any ideas? maybe the conductivity of petrol can be used?

Depending on where you live, a 60-mile buffer doesn't seem such a bad
idea!

I'd avoid conductivity: don't mess with anything that has the
remotest chance of igniting the fuel. I'd first (assuming I really
cared) check to see if the existing sensor was useable. It may just
be the readout part that's giving you fits. If not, I'd probably just
shrug and live with it...but you might consider something that
measures the weight of the tank+fuel, and subtract off the tank weight
(tare). It might be possible to do it with an ultrasonic distance
measurement, too.

Cheers,
Tom
 
Z

Zak

Jan 1, 1970
0
Tom said:
It might be possible to do it with an ultrasonic distance
measurement, too.

I thought about that one for european rental cars. Fuel is expensive
here, so it matters quite a bit how much fuel is in it when you return
it. The dash meter obviously isn't enough - not in any case for giving
the car out to the next renter with the promise that any difference when
returning will be calculated at some average price.

Thus the car gets filled up by personnel at some huge markup which
people then dislike.

Now, a calibrated cheap ultrasonic meter would be a nice add-on. You
couldn't return the car totally empty, and the price calculated would be
a tad higher than market to encourage returning with a full tank.

But if it can work? Especially calibrating only once per vehilcle type.


Thomas
 
Z

Zak

Jan 1, 1970
0
M.C.D. Roos said:
http://www.fw-systeme.de/Downloads/OilCheck4.1.pdf

Important components are membrane pump, pressure sensor and a tube that
drops down to the bottom of the tank. A very nice design, although I
suspect you will see some problems when building this into a car (like
pumping oxygen into your fuel tank).

Fuel tanks are not at atmospheric pressure anyway.

Youd need a second T piece in the cabinet and two hoses to the tank: one
above the fuel leven and one below. Taking care not to suck fuel into
the pump...


Thomas
 
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