Why are automotive fuel gauges [still] so non-linear?

[YeOldeStonecat]

Shouldn't be rocket science in today's world with how computerized our vehicles are.

Open Fuel Filler = re-set
Put in fuel = flow in (flowmeter) calculated
Use gas = flow out (flowmeter) calculated
1st minus 2nd = amount left. calculated

12 gals flowed in and 10 flowed out leaving 2 left????????

Surely I'm missing something?

Temperature and Altitude affect volume of gasoline. Suppose you fill up at sea level..and drive into the mountains. Or visa versa. And toss in temp changes. Up to 20% error (or change in reading really) could be possible.

After roughly a century...I think gas tank gauges do what they're supposed to within expectations.

 

[Krynn72]

Shouldn't be rocket science in today's world with how computerized our vehicles are.

Open Fuel Filler = re-set
Put in fuel = flow in (flowmeter) calculated
Use gas = flow out (flowmeter) calculated
1st minus 2nd = amount left. calculated

12 gals flowed in and 10 flowed out leaving 2 left????????

Surely I'm missing something?

You're missing the part where it costs money to do that on every car and probably ends up being even more unreliable due to sensor failures and such. I mean, have you seen how flaky computers can be? This method works good enough and works every time. It only offends the OCD who cant stand the meter moving around on them.

 

[gikstar]

Incidentally I just took apart my Mercedes C240 fuel pump this weekend trying to figure out why no fuel is going to the engine (turned out to be a relay in the end), but guess what! It's still just a stupid plastic float on an aluminum stick. I'd guess there's just no incentive to make a more accurate fuel gauge. You really think it'd be a selling point to a consumer? I think the color of paint will have a greater impact there.

Right, color, leather seats, heated seats, in-dash GPS, answering your phone and phone charger and lets not forget 'garage door opener' all come with higher priority to a buyer than an accurate fuel gauge (especially on a Mercedes, which the C240 model is my son's company car).

 

[HFultzjr]

Somehow I thought it couldn't be that easy.
Sort of like the progress bar........8 min.........6 min........32 min.......5 min.......40 min........done.

 

[jbartlett323]

We could all still do like my dad's '66 Chevy pickup. Gas gauge is so unpredictable, he puts a stick in it to double check. Often, just ignores the gauge and trusts the stick. Guaranteed to be accurate, up to half an inch!

 

[wolfson]

My current car, for example, has a digital gauge, with little pips that make a kind-of progress meter. There as 12 pips that light up when the tank is full. While the range of the car varies depending on gas mileage, it's fairly typical for me to get 400 miles per tank in the summertime. It can take anywhere between 80 and 115 miles for that first pip to go dark, and the miles per pip as the tank goes to empty seems to be clearly non-linear. I can be at 300 miles for the current tank of gas and the gauge will still read half-full. The last couple of pips can go dark at maybe 20 miles per pip. In my mind, it shouldn't be unreasonable to expect an average "miles per pip" to be about equal to average miles per tank divided by number of pips, you know, linear.

Sounds to me like you have a Prius (I had exactly the same problem). One thing I've heard about these cars in particular, is that the gas tank has some sort of membrane on the inside that expands/contracts depending on the level of gas in the tank, making the gauge less accurate (though I can't confirm whether this is actually true or not). Something that may help (if it's indeed a Prius) is resetting the inclinometer: http://www.import-car.com/tech-tip-toyota-fuel-gauge-inclination-meter-reset/. This made my gauge somewhat more accurate, though still not completely.

 

[Markverhyden]

I've had several GM cars where the gas gauge went bonkers. The faster I drove the more gas it showed it had! LOL!!! At any rate I'm in the habit of resetting my trip odo so I use that as my gauge.

 

[glennd]

The faster I drove the more gas it showed it had!

That explains a few things!

 

[ohio_grad_06]

We just got a 2016 chevy sonic a few months back. It actually has a digital gas guage.

 

[phaZed]

We just got a 2016 chevy sonic a few months back. It actually has a digital gas guage.

Most are all-digital, even though it may have an analogue gauge. Modern gauges are little stepper/servo motors, fed it's indicating position from the computer based on a digital number, derived from a mathematical formula based on the (usually) multiple fuel level sensors.

 

[brandonkick]

I've "owned" two vehicles in my life so far.

When I turned 16, I got to drive my dads 96 chevy blazer. I took over the payments
on that thing and it was mine. Gas gauge wasn't very accurate.

In 2006 I bought a 99 monte carlo with the 3.1 and it's gas gauge hasn't been very
accurate either.

I have however, been using a technique that has NEVER let me down yet.

In the course of owning and driving both vehicles I quickly got a rough estimate of
how many miles per gallon each vehicle was getting. It's fairly simple. Reset the trip
meter when you pull in to get gas. Then all you have to do is fill the gas tank
full until the gas pump stops and then drive for some period of time. I like to try
to wait until I feel the tank is reasonably half empty. I then go back to the gas station
and fill the tank again until the pump kicks off and do not top it off. I then look at the
pump and see how much gas was put in.

Simple math lets you divide the number of miles driven, by the gallons of gas needed
to get the tank back to full and you now have a reasonable estimate of gas mileage.
From there, it's as simple as finding out how big your gas tank is and then using the
trip meter as your gas gauge.

I know that my monte carlo gets about 200 miles per tank. A little less if it's all city driving
and a little more if it's a lot of highway driving.

My rule of thumb is to fill the tank when I start getting over 150 miles on the trip meter.

The gas gauge can stop working period and I'd be A OK.


Just because my mind tends to be so highly analytical, I am almost always re figuring how
many miles per gallon I'm getting at a fill up. Can be a nice indication if you notice wildly
lower gas mileage (with reasonably similar driving habits) and can be a good indication that
your gas station is getting cheaper with the quality of the gas or more so what they are adding
into it.

Once or twice I could really tell it was time for a tune up, I lost about 5 MPG's and noticed that
the gas station itself didn't make a difference in my MPG's. Did a tune up and all of it came back.
Also noticed over time that the main gas station I was getting gas at was getting worse and worse.
I had started to attribute it to my car being almost 20 years old now, but I found when I went to a
smaller independent gas station that charges 10-15 cents more per gallon that not only does my
car run a lot better but it also gets decently improved mileage.