How accurate are gas pumps?

[KFC911]

Put 25.9 gallons in my 25 gal tank today .
I don't think I was on fumes either...always push the limit, and only on one other occasion have I ever topped 25 before. I know they are "supposed" to be accurate at any pressure, etc. but how do we know for sure?

Now I want to put 26 gals in...living on the edge

[Gogar]

It's totally fun until that time you guess incorrectly!!!

Good question though. I assume there's some kind of allowable tolerance.

[vonsmog]

I know that here in NY the state certify that they are pumping the posted amount. And if not the station will be fined big time. They send inspectors around to check out the pumps.

[pen15]

Your tank is not 25 gallons. It is designed to fit the space allotted for it not to hold a nice round number. I have removed tanks from cars and trucks that read well below empty and still contain a gallon or two of fuel. The filler neck itself can hold a gallon and the design of most tanks leave an air space at the top. I would guess the actual volume of a 25 gallon tank is more like 27-28.

[rwest]

Originally Posted by vonsmog

I know that here in NY the state certify that they are pumping the posted amount. And if not the station will be fined big time. They send inspectors around to check out the pumps.

Few years back, they discovered a scam where the pumps were set to accurately dispense the quantities that the inspectors tested for, but shorted quantities over and under.

I think the testing has been changed to use random fill amounts now, but not for sure on that.

[Arizona_928]

I'm sure there's a hotline where you can report, or file a complaint through the inspector office?

[stomachmonkey]

Regularly running around with your tank that low is a great idea if you enjoy replacing fuel pumps.

Fuel pumps are cooled by the gas they are submerged in.

When you run too low they overheat leading to premature failure.

One thing in a car where typically you can access it from inside the car.

Quite another in trucks / SUVs where a tank drop is required.

YMMV

[BK911]

In one of my undergrad design classes, the instructor said that gas pump meters were one of the worst types of meters available. I have personally pumped 5.5 gallons into a 5 gallon can.

[Saadi996tt]

As a owner of a gas station, I can assure you that the gas flows in the great republic of California are tested, monthly (we hire a compliance company to test), quarterly (compliance co & county inspector), and annually ( compliance & county inspector). So in all we are tested 17 times a year. The temperature can also play a role in volume of gas dispensed...


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[wdfifteen]

In Ohio the county is responsible for testing the pumps. The pumps have calibration stickers on them that are dated, but to tell the truth I've never looked at them closely enough to see the dates, but I think they are tested annually. They fill a calibrated 5 gallon container and must be within .5 percent of accurate to pass.

[sammyg2]

In the United States, the National Institute of Standards and Technology (NIST) specifies the accuracy of the measurements in Handbook 44. Table 3.30 specifies the accuracy at 0.3% meaning that a 10-US-gallon (37.9 L; 8.3 imp gal) purchase could vary between 9.97 US gal (37.7 L; 8.3 imp gal) and 10.03 US gal (38.0 L; 8.4 imp gal) as to the actual amounts at the delivery temperature of the gasoline.

So in conclusion, they are very ****ing accurate.

[sammyg2]

Originally Posted by BK911

In one of my undergrad design classes, the instructor said that gas pump meters were one of the worst types of meters available. I have personally pumped 5.5 gallons into a 5 gallon can.

That is probably a good example of why he is an instructor and does not make a living in the real world.

The positive displacement volumetric meter used to measure fuel at the pumps is very accurate, very predictable, simple and holds calibration for a long time.

It would make allot more sense to question the accuracy of your 5 gallon can.

[Por_sha911]

Originally Posted by BK911

In one of my undergrad design classes, the instructor said that gas pump meters were one of the worst types of meters available. I have personally pumped 5.5 gallons into a 5 gallon can.

Go back and look at the can. It has a fill level. You can easily put a 1/2 gallon in above that level if you pump it to the top.

[KFC911]

Originally Posted by stomachmonkey

Regularly running around with your tank that low is a great idea if you enjoy replacing fuel pumps.

Fuel pumps are cooled by the gas they are submerged in.

When you run too low they overheat leading to premature failure.

One thing in a car where typically you can access it from inside the car.

Quite another ivn trucks / SUVs where a tank drop is required.

YMMV

I know all of this, yet I'm not changing my ways after 40+ years of driving and at least 200 fill ups in that truck with less than a gal to spare
Did completely run out one time as I rolled into the station, but didn't fill up that particular time. I also realize the capacity is more than 25, but I still think that particular pump wasn't calibrated properly based upon the fuel guage reading and prior history/track record of 24+ gal fill ups...jmo

One of these days I may be posting another "sofa king" thread....until then, I'll be

Living on the edge

[TheMentat]

Originally Posted by sammyg2

So in conclusion, they are very ****ing accurate.

cool video!

[stevej37]

Not trying to divert this thread...but what about the pricing on the diff grades of gas?
A few years back there was always a 40 cent diff from reg to prem. Lately that diff has changed to 60 cents. This past week when filling up..I found a $1.00 diff from reg to prem. What is going on??

[sammyg2]

Originally Posted by stevej37

Not trying to divert this thread...but what about the pricing on the diff grades of gas?
A few years back there was always a 40 cent diff from reg to prem. Lately that diff has changed to 60 cents. This past week when filling up..I found a $1.00 diff from reg to prem. What is going on??

Dated, but informative:

May 6, 2013
Price spread between regular and premium gasoline has changed over time
Graph of premium versus regular U.S. gasoline prices, as explained in the article text
Source: U.S. Energy Information Administration.


The difference between the U.S. average retail price for premium and regular gasoline—the premium for premium—reached 30 cents per gallon for the first time at the end of 2012, a level that has been maintained thus far in 2013. However, on a percentage basis, the price spread between premium grade and regular grade gasoline has actually remained relatively stable since mid-2009. With the exception of a spike in late 2008, the percentage spread fell fairly steadily from 17% in 2001 to a low of 6% in early 2008. The decline in the percentage price spread between premium grade and regular grade gasoline over this period coincides with increased blending of ethanol into the motor gasoline pool.

Over the last decade ethanol emerged as an important component of gasoline and provided a considerable source of octane. Ethanol blended into gasoline has an average octane rating of 115, significantly higher than the gasoline octane rating at retail stations for regular (87 octane) and premium (91-93 octane) gasoline. As a result, refineries have been able to decrease the octane level of gasoline blendstock, which will be blended with ethanol to make finished gasoline. The Environmental Protection Agency (EPA) estimates that refiners produce 84 octane blendstock that, when blended with ethanol, will meet the 87 octane minimum for regular-grade gasoline, and produce 88 octane blendstock that will meet a 91 octane premium-grade finished gasoline requirement after blending.
Graph of gas price differential and ethanol blending percentages, as explained in the article text
Source: U.S. Energy Information Administration.


For a refiner, there is a tradeoff between octane levels and volume of gasoline produced: higher levels of octane reduce production volume, raising the relative price of higher octane fuels. This tradeoff is not linear, and production declines more rapidly as octane increases. As a result, more cost savings result from reducing octane levels for premium gasoline blendstock (91 octane to 88) than from reducing the already lower regular gasoline blendstock octane levels (87 to 84). As the percentage of ethanol in gasoline grows, higher octane blendstock becomes relatively cheaper, reducing the percentage-based grade differential for premium versus regular gasoline.

In addition to ethanol's impact on the relative decline in premium gasoline production costs, the changing price relationship between premium and regular gasoline may reflect other factors. Consumption of premium gasoline has declined for more than two decades, possibly making premium a less competitive fuel from a pricing standpoint.

For additional information see EIA's assessment in This Week in Petroleum.

U.S. Energy Information Administration (EIA)

[sammyg2]

Originally Posted by KC911

I know all of this, yet I'm not changing my ways after 40+ years of driving and at least 200 fill ups in that truck with less than a gal to spare
Did completely run out one time as I rolled into the station, but didn't fill up that particular time. I also realize the capacity is more than 25, but I still think that particular pump wasn't calibrated properly based upon the fuel guage reading and prior history/track record of 24+ gal fill ups...jmo

One of these days I may be posting another "sofa king" thread....until then, I'll be

Living on the edge

In my YOOT I was much the same way. I wouldn't fill up until I absolutely had to.

Then I paid for a new fuel pump and two new catalytic convertors on my 86 for furd ranger and decided running on fumes was a bad thing.

Nowadays I rarely get under 1/4 tank (approx. 7 gallons). I figure one of these days the big one is gonna hit, and assuming I can find roads open I want to have the ability to drive from work to home or home to ????? without having to loot some gas 'cause all the pumps will be down.

Who knows how long that drive might take, but the worst case scenario would be to get stranded in long beach after a major quake with looting and such, and not have any gas or spoons or ammo to take out the zombies and dips

Since we have 4 cars (me, wifey, daughter, son) I figure at any one time I can siphon together at least one whole tank of fuel but I'd still have to get home to get it (32 mile drive).

I rarely hear anyone say "I wish my gas tank wasn't so full" ....

[Cajundaddy]

Gas meters are pretty damn accurate but...
Gas volume changes quite a bit with changes in temperature. Hint: Fill up in the morning.

Also, the teenager that filled ahead of you may have shut off the pump and gravity-drained another 1/2 gallon from the hose into his tank. When you started, the pump had to refill the hose first before getting gas into your tank. (don't ask how I know this trick) .

[speeder]

I hate to say it but Sammy is right in this thread.

Also, I'm only seeing the usual ten cent difference between grades of gas here in Los Angeles, for the most part. The exception would be a loss leader station downtown that is giving away 87 octane to have that lowest price sign up but making up for it on mid and premium which are 50 cents more.

My dad was a *keep stocked up* kind of guy and he always had a year's supply of paper towels, toothpaste, etc. When his car got down to half a tank, he had to fill it. No exceptions. Like he had a phobia about running out of anything. I'm not like that but I don't test my fuel gauges like I did when I was young and broke, either.