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,

Reply to
cpliu
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The newer cars have a somewhat more accurate method of measuring gasoline usage, but it is far from perfect.

Older cars had some version of a float in the tank and its position was estimated by a potentiometer. It was only indicative and was not very quantitative.

The newer ones take measurements based on the fuel injector operation. More accurate, but not great.

For your car, fill it up, drive a number of miles and then refill the tank. It isnt perfect either, but will be a heck of a lot more accurate than what you are trying to do,.

Reply to
hls

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

Reply to
Scott Dorsey

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.
Reply to
Paul in Houston TX

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

Reply to
AMuzi

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. :-)

Reply to
dsi1

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.
Reply to
Hachiroku $B%O%A%m%/(B

Cold starts and short trips use a lot of gas

Reply to
bugalugs

cpliu wrote in news:889a2096-d189-4f00-9993- snipped-for-privacy@32g2000vbe.googlegroups.com:

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.

Reply to
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.

Reply to
liu

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

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

Reply to
jim

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. :^/

Reply to
aemeijers

Just a warning to all those Camry owners out there who are still filling the tank completely to calculate fuel economy: the vapor recovery system is likely to fail, and the filler pipe start leaking. After battling these issues for several years we now just fill it

*almost* all the way. Problems solved. You can prevent them the same way. You don't get an exact fuel economy reading, but if you already know what the car averages, you can use the odometer to make sure it hasn't suddenly started guzzling gas.
Reply to
Leftie

Hasn't this been the case for just about every car made since the late eighties? It's not anything specific to the Camry.

--scott

Reply to
Scott Dorsey
0) to (1) = ~2 gallons

WOW US$60 to fill up if I read that correctly. What a bargain.

I have a 1995 4 banger. Had it since new. 105.000 miles.

15 Gallon tank , so that's 15 X 4.5 for litres. 1 litre = GB£1.35 = US$2.16 15 gallons = 67 litres. Fill up costs GB£91 = US$145.

What can I say but ***********************

Johnny UK

Reply to
Johnny Melvin

I would add that, since this incarnation of the Camry is prone to filler pipe and vapor recover canister problems, you don't actually fill it completely. Just wait until you hear the sound of the air rushing out of the filler change pitch, and stop right there. Again, once you get the hang of it any errors will average out over time.

Reply to
Leftie

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