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  Topic Review (Newest First)
03-29-2019 07:04 AM
plano-doug
Quote:
Originally Posted by Joes74challenger View Post
on newer cars i always thought that was the point of why the gauges all peg then return to 0 and back up to the actual reading at each ignition key initial cycle? i thought they self calibrated already?
What you describe is the gauge reflecting the position of the level sensor. The calibration I was talking about was how well the level sensor position reflects the actual volume left in the tank. Calibrating the level sensor would entail filling the tank to 3 or more known volumes of fuel and taking readings from each.

For sure, this cannot be done on each car in production.

Instead, I suspect something like this is done to several cars during product testing - maybe 100, maybe more - to characterize the gas gauge system. From that they will derive the typical values, and use those numbers to set up the relationship between level sensor (voltage) and the gauge.

But I'm sure the variances on this system are way wider than, for example, cylinder bore dimensions That is, the real world tolerances on the fuel level will be on the order of 1 gallon, but if it could be calibrated with cylinder bore accuracies, it would be on the order of 1 teaspoon

Doug

.
03-29-2019 06:33 AM
Joes74challenger
Quote:
Originally Posted by plano-doug View Post
Keep in mind, that's not all by design. Some of it is just the nature of fuel systems. There are large areas of material (sheet metal, in the old days ) that can flex and take somewhat different shapes in different cars resulting in a gallon or so of difference in volume, for the same position of the float in the level sensor.

In a high end system - think airplane maybe - during production, they might calibrate each fuel level sensing system. But in the car world, it's probably a deal breaker of a cost adder. The result is that one person's 130 miles left in the tank is another's 13 miles left in the tank

I swear, in my 1974 F-100, once it got so low, the needle would actually start creeping back up and give me a bum steer

Doug

.
on newer cars i always thought that was the point of why the gauges all peg then return to 0 and back up to the actual reading at each ignition key initial cycle? i thought they self calibrated already?
03-28-2019 02:06 PM
USN24 I do believe the light comes on before you are truly empty to keep the average person from running out of gas. I wish I was average sometimes.
03-28-2019 01:27 PM
plano-doug
Quote:
Originally Posted by Mike55 View Post
Thanks everyone for the insight! I typically don't run my vehicles past a quarter tank but noticed that at a quarter tank I had 130 miles left on the info screen which I felt was high so I ran a test 🙂 kinda wish they didn't do this. I'm competent enough to not run my vehicle dry and I'd rather see the true fuel level in the gauge but alas they had others in mind when designing the fuel gauge.
Keep in mind, that's not all by design. Some of it is just the nature of fuel systems. There are large areas of material (sheet metal, in the old days ) that can flex and take somewhat different shapes in different cars resulting in a gallon or so of difference in volume, for the same position of the float in the level sensor.

In a high end system - think airplane maybe - during production, they might calibrate each fuel level sensing system. But in the car world, it's probably a deal breaker of a cost adder. The result is that one person's 130 miles left in the tank is another's 13 miles left in the tank

I swear, in my 1974 F-100, once it got so low, the needle would actually start creeping back up and give me a bum steer

Doug

.
03-28-2019 01:01 PM
jtrosky
Quote:
Originally Posted by sheila View Post
I've always told my 3 sons, "If you're down to a 1/4 tank, you're empty. Do they listen? Hell no!" Lol!!!
Not only that, but now they probably TRY to get it below a 1/4 tank on purpose, just to prove you wrong! ;-)

Yes, I have a know-it-all 17 year old son too... :-)
03-28-2019 12:54 PM
kbz1960
Quote:
Originally Posted by sheila View Post
I've always told my 3 sons, "If you're down to a 1/4 tank, you're empty. Do they listen? Hell no!" Lol!!!
Of course not! [emoji16]
03-28-2019 12:19 PM
sheila I've always told my 3 sons, "If you're down to a 1/4 tank, you're empty. Do they listen? Hell no!" Lol!!!
03-28-2019 08:21 AM
Mike55 Thanks everyone for the insight! I typically don't run my vehicles past a quarter tank but noticed that at a quarter tank I had 130 miles left on the info screen which I felt was high so I ran a test 🙂 kinda wish they didn't do this. I'm competent enough to not run my vehicle dry and I'd rather see the true fuel level in the gauge but alas they had others in mind when designing the fuel gauge.
03-28-2019 07:26 AM
plano-doug
Quote:
Originally Posted by Joes74challenger View Post
also a side note, running a fuel pump down like that may not be the best for it, it uses the fuel to cool itself so when it starts sucking air from a lack of fuel in the tank it may start overheating some and cause a potential loss of life. keeping it around 1/4 tank or higher would prevent such an issue.
Furthermore, running it low means it's more likely to suck up dirt and debris floating on the surface, which can clog things up.

(That probably explains the clogged fuel filter in my first vehicle, which rarely got _above_ a quarter tank )

Doug

.
03-28-2019 06:13 AM
Joes74challenger in the atv world they make a secondary pickup that gives you another .7 gallons or something similar to that as a reserve for when you run out (a lot of them don't have gas gauges). i think the auto makers are doing the same thing, they have that gas light come on to tell you get to a station asap but you still have a couple of gallons left in the tank. the pic of the gas pump in the digital display is the same in all chevy's i've seen, it is a stationary image and doesn't change levels based on the actual fuel level of the car.

also a side note, running a fuel pump down like that may not be the best for it, it uses the fuel to cool itself so when it starts sucking air from a lack of fuel in the tank it may start overheating some and cause a potential loss of life. keeping it around 1/4 tank or higher would prevent such an issue. again this is theoretical and just a safe practice.
03-28-2019 02:28 AM
impaler About every vehicle I've owned was like that. The gauge will show empty before it really is. Our 15 Impala and our 15 Sierra are the same way.
I haven't noticed the gas pump icon on the display changing on either one.
03-27-2019 08:53 PM
Mike55
2015 Impala Gas Gauge and Info Screen

So I drove my car down to E today... And a couple of things confused me. The gas light did not come on until a second before I took this photo when the vehicle was already on E but the info screen shows I can still drive 47 miles. When I refilled to a full tank I was able to put in 16 gallons. This vehicle has a 18.5 gallon tank so the info screen is right and the fuel gauge appears to be in accurate. Has anyone else noticed this? Also isn't the picture of the fuel tank on the info screen filled in by blue supposed to go up and down with the level of fuel remaining? Why have the little full and half full bubbles underneath it if not? It's always stayed the same half full level for me. Any info would be appreciated!

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