gas gauge reading

I drive a 94 Camry which still works great after 180K miles. I've been
record the gas gauge reading trying to know fuel efficiency in the
past few years.

I'm a little puzzled on how it works and the accuracy of the reading.
My observations:
I suspect the sensor is in the front part of the tank as the gas level
drops when you climbing up the hill, and goes up when driving down the
hill.
The level goes up and down sometimes. In the middle of the driving, it
may go 1 to 2 mm below and it would go up again a few minutes later.
Maybe it relates to the condition of the road?
The level usually drops (and not coming up again) at a bigger distance
than a gradual drop. I may stay on full first. going down and up a few
times, then it drops to 2/3 above the next scale down.
The level location may be the most accurate when you first start up in
the morning. Usually it's a little lower than the previous night. But
it will go up again similar to the previous day due to moving.
I suspect the temperature makes a difference too.

So basically, it's hard for me to really know how much gas I've used
daily thus the MPG, and how much gas exactly is left. Are there new
cars that provide more accurate reading, something similar to MPG
indicator in some of the cars?

Thanks,

cpliu wrote:
> I drive a 94 Camry which still works great after 180K miles. I've been
> record the gas gauge reading trying to know fuel efficiency in the
> past few years.
>
> I'm a little puzzled on how it works and the accuracy of the reading.

Your gas gauge is not linear.
To go from full to 3/4 full will likely take 12 gallons
and from 3/4 to empty will take 6 gallons, leaving
2 gallons in reserve at empty.

cpliu wrote:
> I drive a 94 Camry which still works great after 180K miles. I've been
> record the gas gauge reading trying to know fuel efficiency in the
> past few years.
>
> I'm a little puzzled on how it works and the accuracy of the reading.
> My observations:
> I suspect the sensor is in the front part of the tank as the gas level
> drops when you climbing up the hill, and goes up when driving down the
> hill.
> The level goes up and down sometimes. In the middle of the driving, it
> may go 1 to 2 mm below and it would go up again a few minutes later.
> Maybe it relates to the condition of the road?
> The level usually drops (and not coming up again) at a bigger distance
> than a gradual drop. I may stay on full first. going down and up a few
> times, then it drops to 2/3 above the next scale down.
> The level location may be the most accurate when you first start up in
> the morning. Usually it's a little lower than the previous night. But
> it will go up again similar to the previous day due to moving.
> I suspect the temperature makes a difference too.
>
> So basically, it's hard for me to really know how much gas I've used
> daily thus the MPG, and how much gas exactly is left. Are there new
> cars that provide more accurate reading, something similar to MPG
> indicator in some of the cars?


A fuel gauge is not useful for that purpose.

Fill tank, record mileage.
On next fill, note fuel volume used and distance traveled.

If one keeps a simple log, any errors get smoothed after
more fill iterations

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On 6/3/2011 3:36 AM, cpliu wrote:
> I drive a 94 Camry which still works great after 180K miles. I've been
> record the gas gauge reading trying to know fuel efficiency in the
> past few years.
>
> I'm a little puzzled on how it works and the accuracy of the reading.
> My observations:
> I suspect the sensor is in the front part of the tank as the gas level
> drops when you climbing up the hill, and goes up when driving down the
> hill.
> The level goes up and down sometimes. In the middle of the driving, it
> may go 1 to 2 mm below and it would go up again a few minutes later.
> Maybe it relates to the condition of the road?
> The level usually drops (and not coming up again) at a bigger distance
> than a gradual drop. I may stay on full first. going down and up a few
> times, then it drops to 2/3 above the next scale down.
> The level location may be the most accurate when you first start up in
> the morning. Usually it's a little lower than the previous night. But
> it will go up again similar to the previous day due to moving.
> I suspect the temperature makes a difference too.
>
> So basically, it's hard for me to really know how much gas I've used
> daily thus the MPG, and how much gas exactly is left. Are there new
> cars that provide more accurate reading, something similar to MPG
> indicator in some of the cars?

Your gas gauge gets more responsive towards the bottom of the tank.
Designing the gauge like this will give you a better idea of how much
gas is left in your tank.

My 2006 Hyundai has a resetable trip calculator that gives MPG reading.
I get around 14 MPG because my workplace is about a mile and a half
away. On long trips, I can get 24 MPG easily. It also gives average
speed. Mine is 14 miles per hour - seriously. :-)

>
> Thanks,
>
>

On Fri, 03 Jun 2011 11:35:40 -0400, Scott Dorsey wrote:

> cpliu > wrote:
>>So basically, it's hard for me to really know how much gas I've used
>>daily thus the MPG, and how much gas exactly is left. Are there new
>>cars that provide more accurate reading, something similar to MPG
>>indicator in some of the cars?
>
> No. All you can do is fill your tank up every day and check how much gasoline
> has gone into it to make it full.
>
> The gas gauge is only there to keep you from running out of gas, it's not
> anything even remotely approaching linear or consistent. It doesn't have
> to be.
> --scott


But not every day. I generally let it go 150-200 miles to get an accurate
reading.

Don't ask me why, but filling it every day give me a lower reading than
going a couple hundred miles. Especially if I'm doing short trips.

I notice on weekends, when I rarely venture more than 5 miles from home,
mileage on my '89 Mazda 626 is ~28-30. During the week, when I drive 20
miles or more at a clip (over the same type roads, not the highway) I get
31-33.

On 4/06/2011 12:02 p.m., Hachiroku ãƒ�ãƒ�ãƒ*ク wrote:
> On Fri, 03 Jun 2011 11:35:40 -0400, Scott Dorsey wrote:
>
>> > wrote:
>>> So basically, it's hard for me to really know how much gas I've used
>>> daily thus the MPG, and how much gas exactly is left. Are there new
>>> cars that provide more accurate reading, something similar to MPG
>>> indicator in some of the cars?
>>
>> No. All you can do is fill your tank up every day and check how much gasoline
>> has gone into it to make it full.
>>
>> The gas gauge is only there to keep you from running out of gas, it's not
>> anything even remotely approaching linear or consistent. It doesn't have
>> to be.
>> --scott
>
>
> But not every day. I generally let it go 150-200 miles to get an accurate
> reading.
>
> Don't ask me why, but filling it every day give me a lower reading than
> going a couple hundred miles. Especially if I'm doing short trips.
>
> I notice on weekends, when I rarely venture more than 5 miles from home,
> mileage on my '89 Mazda 626 is ~28-30. During the week, when I drive 20
> miles or more at a clip (over the same type roads, not the highway) I get
> 31-33.
>
>


Cold starts and short trips use a lot of gas

--
A bus station is where a bus stops. A train station is where
a train stops. On my desk, I have a workstation.

cpliu > wrote in news:889a2096-d189-4f00-9993-
:

> I drive a 94 Camry which still works great after 180K miles. I've been
> record the gas gauge reading trying to know fuel efficiency in the
> past few years.
>
> I'm a little puzzled on how it works and the accuracy of the reading.
> My observations:
> I suspect the sensor is in the front part of the tank as the gas level
> drops when you climbing up the hill, and goes up when driving down the
> hill.
> The level goes up and down sometimes. In the middle of the driving, it
> may go 1 to 2 mm below and it would go up again a few minutes later.
> Maybe it relates to the condition of the road?
> The level usually drops (and not coming up again) at a bigger distance
> than a gradual drop. I may stay on full first. going down and up a few
> times, then it drops to 2/3 above the next scale down.
> The level location may be the most accurate when you first start up in
> the morning. Usually it's a little lower than the previous night. But
> it will go up again similar to the previous day due to moving.
> I suspect the temperature makes a difference too.
>
> So basically, it's hard for me to really know how much gas I've used
> daily thus the MPG, and how much gas exactly is left. Are there new
> cars that provide more accurate reading, something similar to MPG
> indicator in some of the cars?
>



You cannot use the gas gauge as an indicator of mileage except in the
broadest, crudest manner (as in, "Am I going to run out of gas in the next
few minutes?").

The gas gauge employs a float that bobs up and down on top of the gas in
the tank. The float is connected to a lever that moves a contact back and
forth on a potentiometer (a special resistor). The changing location of the
contact results in a varying electrical current that is interpreted by the
gas gauge as a particular needle-reading.

As you drive, your gas is sloshing all over the place in the tank, and that
little bobber is bouncing all over the place like a pirate ship in a storm.
That's a problem. Left as-is, the bobber would cause your gas gauge needle
to also bounce all over the place. How automakers fix that is to install
some special electrical components in the circuitry. These components damp-
out most of that bobbing, so instead you see a s-l-o-w and steady change up
or down in the condition of the gauge needle, these changes corresponding
to you going up and down hills, or around corners.

When those damping components fail, the gas gauge turns into a weebly-
wobbly, bouncy-flouncy, wiggly bunch of useless fun, readable only when the
car is completely motionless and level. You come to appreciate the damping
when it's not there anymore.

If you want to accurately record your gas mileage, ignore that gas gauge
entirely. AMuzi has the correct idea, so see his message.

--
Tegger

Thank you all for the information. I'm trying to figure out a way to
make a pretty good guesstimate on how much gas has been used and left
by looking at the location of the needle. It looks like I'm not going
to reach a very accurate reading.

I calculate my MPG every time I fill up the gas tank (BTW, my 1994 4
cyl. is a little over 40mph highway at 60MPH, 25 o 27 mph city at
earlier traffic time). I also made a record on the location of the
needle before adding the gas and after adding the gas.
Based on my record of before-and-after needle positions, I estimated
the following
empty to (0) = ~2 to 2.5 gallons
(0) to (1) = ~2 gallons
(1) to (2, mid point) = ~4 gallons
(2) to (3) = ~ 6 gallons
(3) to (4) = ~ 4 gallons
2 more gallons you can add after it reaches the top.

Because I can never tell accurately when it actually reach each scale,
my numbers are probably off.

Tegger wrote:

> >
>
> You cannot use the gas gauge as an indicator of mileage except in the
> broadest, crudest manner (as in, "Am I going to run out of gas in the next
> few minutes?").

Yup. It is even dumber to use dipstick measurements to calculate oil
consumption.

>
> The gas gauge employs a float that bobs up and down on top of the gas in
> the tank. The float is connected to a lever that moves a contact back and
> forth on a potentiometer (a special resistor). The changing location of the
> contact results in a varying electrical current that is interpreted by the
> gas gauge as a particular needle-reading.

Well if that were the problem you could just
park the car on level ground when you need to get a good reading

On 6/3/2011 10:22 PM, liu wrote:
> Thank you all for the information. I'm trying to figure out a way to
> make a pretty good guesstimate on how much gas has been used and left
> by looking at the location of the needle. It looks like I'm not going
> to reach a very accurate reading.
>
> I calculate my MPG every time I fill up the gas tank (BTW, my 1994 4
> cyl. is a little over 40mph highway at 60MPH, 25 o 27 mph city at
> earlier traffic time). I also made a record on the location of the
> needle before adding the gas and after adding the gas.
> Based on my record of before-and-after needle positions, I estimated
> the following
> empty to (0) = ~2 to 2.5 gallons
> (0) to (1) = ~2 gallons
> (1) to (2, mid point) = ~4 gallons
> (2) to (3) = ~ 6 gallons
> (3) to (4) = ~ 4 gallons
> 2 more gallons you can add after it reaches the top.
>
> Because I can never tell accurately when it actually reach each scale,
> my numbers are probably off.
>

Like others said, forget the gauge- use post-it notes or the trip
odometer, if you have one. Run it near empty, record the miles on the
clock. Run it near empty again, and record the miles again. The
difference is your maximum miles before you start looking for an open
gas station. Fill it every time, and record the miles every time. When
the odometer says you are getting near your empty point, fill up. I
tend to top off when the gauge gets below half, in case price spikes,
and so I don't have to think about it. That, and $60+ fillups depress
the hell out of me. :^/

--
aem sends....