Are gas pumps calibrated?

S

Stuck_At_Work

1,000+ Posts
... by a third party?

I know for a fact that my car's gas tank holds 14 gallons. When the light comes on, it usually takes somewhere between 12.8 to 13.6 gallons to fill it up. I've driven the car for 4 years and it has never needed more than 13.6 and that is after driving with the warning light on longer than I should have.

Last week, I pulled into a gas station to fill up. The light had just turned on... and the pump claimed to have pumped 14.4 gallons.

Total BS.
 
They are checked by the Department of Agriculture. See if the station you were at is on this list of noncompliant stations.

Link
 
I didn't see any Travis County stations on that list.

The gas station as right at the exit of Austin Bergstrom Airport right as you turn North on 71 to head back into the city. I assume that is Travis county.
 
Yes, they are inspected by a state agency, but there are cases of tampering and fraud.
But sometimes you don't fill the tank quite as much one time, and then put a little more in the next time, and you think your mileage has decreased, or something is wrong when it really isn't. Most people don't accurately measure mileage each time they fill up.
But the station could be cheating people, it is possible.
 
With a lot of the more computer controlled / monitored cars we have these days, you would think that identifying how much fuel you can take should be easier.

The guys on my roofing crew have a diesel dualie that tells you how many miles you have left 'til dry; this should give you a good guess as to how much fuel is left vs. how much you take on.

IIRC, your owner's manual should tell you how many gallons your tank holds & I think it's something you could find online as well.

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I DO know how many gallons my tank holds. The specs say 14. I have never even come close to hitting 14. This particular gas pump says I filled it up with 14.4 gallons.
 
Your tank will hold a little more than the rated capacity due to the amount the filler neck and hose can hold. So if really on fumes, a 14 gallon tank will take a few more tenths of a gallon than 14.0. But you might be right, the pump might be off, deliberately or accidentally, and you could make a complaint.
 
Some new cars have a "bladder" rather than an old school steel tank. It is supposed to reduce emissions and minimize hazardous build up of flammable gasses. This can vary the volume that can be filled.
 
but he said that the light had just come on, so that would indicate that he was not on fumes but had at least a gallon left.

sounds fishy to me.
 
I've put approximately 19 gallons in my 15.8 gallon tank on many occasions from many different pumps. I tend to top off if I'm going to be burning some of the fuel right away, so that explains part of it. Nonetheless, the tank capacity is clearly understated on my vehicle.
 
Please forgive me if I am off on the specifics. But the state of Texas weights and measure department measures how much gas is dispensed at fixed intervals - 5, 10 and 15 gallons for instance. It is possible to program a fuel pump to perform as follows.

Between 0 and 4.5 gallons it always reads high, and then it corrects and reads exactly 5 gallons, at 5 gallons. The same thing happends between 5 and 10 and between 10 and 15 - it always reads the correct amount at the value the state checks, but it always reads high at all values in between. Above 15 it always reads high.
 
Given the amount of money at stake with the cost of gas, I can almost see the day coming when gas pumps will revert to the style of 80 years ago...a measured clear container that fills and then dumps the fuel in the tank. Either that, or we are going to need a shitload of new fuel pump inspectors to keep pace with the scammers.
 
Also, remember your tank holds 14 gallons of gas at a certain temperature, If yor tank holds 14 gallons at 90 degrees, it could easily hold 15 gallons tanks, neck and hose) if the gas was a 60 degrees.
 
that seems like an impossible ammt of volume increase fievel.

i dont think that is whats going on here. arent volumetric changes trace ammts at best?
 
Didn't mythbusters or someone dispel the myth of increased gas volume at varying temperatures? I heard they tested filling up tanks at varying times of the day and in various temperatures....the resulting volume of gas was almost exactly the same. Something about the tanks being buried too deep for temperature to actually make a difference.

I dunno....someone do a search.
 
I was also adding in the neck and the hoses for most of that increase. As far as it being underground, that would make , I would have to look into that more.
 
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