Gas consumption question

Biff Hardslab

I have the t-shirt
Jan 15, 2007
4,517
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#1
Maybe one of you that knows about this can answer this. Why does the fuel gauge in every car I've owned creep to the half tank mark from full and then races to empty? I had 198 miles on the trip odometer at half a tank. Math would say I should get another 198 miles from the other half a tank. But at just under a quarter tank, I'm at 278 miles. I'll probably get a little over 300 when the fuel light comes on. Where's the other 50+ miles of gas that I got from first half a tank?
 
Apr 30, 2011
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CLT
#2
Car manufacturers design the guage to stay on full longer than it really should. Recall reading that this was customers preference.
 

gleet

What's black and white and red all over?
Jul 24, 2005
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#3
 

ysr50

Well-Known Member
Donator
Apr 20, 2012
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#5
I always thought that with a float type sending unit, the float moves more as it nears empty because it's getting closer to moving horizontally and not vertically. Do newer cars even have float type sending units anymore?
 

gleet

What's black and white and red all over?
Jul 24, 2005
22,543
13,852
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Idaho
#7
No, you see, it does have gas in it. I just want to know why the gas gauge moves faster after half a tank.
Once in a great while my 2016 Effin250 will show half or more as I leave town. Plenty for the day's activities. Then within a half hour, it's down to 1/4 or less and I gotta think about finding gas that's 80 miles away or using the 5 gallon can I haul.

It tells how far to empty and I once fueled with it showing 1 mile.
 

THE FEZ MAN

as a matter of fact i dont have 5$
Aug 23, 2002
41,795
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#8
There is a "can" inside the tank, that is not as tall as the tank, the float goes to the top of the can but not the tank, you are always better off following your trip odometer
 

Ballbuster1

In The Danger Zone...
Wackbag Staff
Aug 26, 2002
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#9
I always thought that with a float type sending unit, the float moves more as it nears empty because it's getting closer to moving horizontally and not vertically. Do newer cars even have float type sending units anymore?
Yes and yes.

It's basic geometry. The float usually pegs out before
a tank is full. Then it drops off of full and slows down
at mid tank due to the float being almost level. As it nears the
end of the tank it's pointing down a lot and the vertical drop
is much quicker.
 

Wrecktum

Tounge puncher of fart boxes
Jun 29, 2006
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#10
Also it depends on the shape of your fuel tank. Most tanks are just larger at the top and tend to have recesses at the bottom to make room for lines, exhaust , and drive shafts.
 

steve500

Registered User
Oct 20, 2008
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#11
Yes and yes.

It's basic geometry. The float usually pegs out before
a tank is full. Then it drops off of full and slows down
at mid tank due to the float being almost level. As it nears the
end of the tank it's pointing down a lot and the vertical drop
is much quicker.
Also it depends on the shape of your fuel tank. Most tanks are just larger at the top and tend to have recesses at the bottom to make room for lines, exhaust , and drive shafts.
Why wouldn't the programming account for that though? I've seen this a lot on Jap and American cars, Hyundai is a bit better, and BMW does a much better job
 

5skin

Registered User
May 14, 2010
1,202
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the woods
#12
Momentum, you have more of it when your tank is full making it more fuel efficient to keep moving. As you burn fuel you lose weight and momentum.
 

Wrecktum

Tounge puncher of fart boxes
Jun 29, 2006
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Cervix spelunking
#14
Why wouldn't the programming account for that though? I've seen this a lot on Jap and American cars, Hyundai is a bit better, and BMW does a much better job
I'm sure on some higher end cars. But most car fuel senders are just a plastic float on a metal arm attached to a basic sensor. The sensor just reads the position of the arm. So you're fuel gauge is just a estimate at best.