Temperature effect on pumping gasoline?

[Patman]

With most (if not all) gas stations now listing that the volume of gas you pump is corrected to a certain temperature, I wonder how much of a factor this might be when trying to figure out your MPG?

For instance, if I fill up one time when the temperature is 40 degrees and then the next time I fill up it's 80 degrees, can I even expect my MPG calculations to be anywhere near accurate, or will that much of a temperature variation completely throw off my numbers?

I say this because I'm trying to fine tune my Scangauge to be as close to accurate as possible, but I wonder if I'll ever get there because it just seems like there are so many obstacles out there preventing me from getting 100% accuracy on my manual fillups. For instance, I use the same pump at the same gas station every time, however I do notice that some days it seems like the gas pumps out slower, depending on how many other cars are using that station at the same time, so that factor, combined with the temperature factor, makes me wonder if getting an accurate manual MPG reading is even possible (and maybe I should just leave my Scangauge as is right now and just trust it's MPG readings the most since they won't be affected by those other factors)

 

[HerrStig]

Gas stations in some areas with acidic soil often had their tanks on platforms, above ground. In the South the contents got pretty hot in the summer. I remember a consumer pubby suggesting you always buy gas in the early mourning to get a "full gallon". Waiting in line at a fuel point at Fort Benning long ago, my driver and I watched a Duce and a half back into a pump connected to an elevated tank and knock it over. A fountain of gas resulted. We, ah, "relinquished" our spot in the line....

 

[SteveSRT8]

Patman, I have often wondered about this also.

Obviously a gallon at 80 degrees is less than a gallon at 40 with such a volatile fuel.

In our area all the tanks are underground, so I guess the temps are nearly the same year round.

 

[yonyon]

Trying to fill up a common passenger car's tank to exactly the same level every time is [censored] near futile. You're not going to be able to account for the 15 mph wind from the northeast or the pebble that was under the left front tire last week or the filter in the dispenser that was replaced at 5AM that morning. A variation of a half gallon is pretty common.

 

[doitmyself]

It seems that Canada uses temperature compensating meters to pump their gasoline:

http://strategis.ic.gc.ca/eic/site/mc-mc.nsf/eng/lm04344.html

"Automatic temperature compensation is a more accurate and equitable method of measuring gasoline as it removes the effect of temperature on the volume of gasoline. The purchase and sale of gasoline based on a common reference temperature allows gasoline retailers to sell product on the same basis as it was purchased (facilitating accurate product inventories and early detection of product loss). The use of gasoline pumps equipped with automatic temperature compensation benefits consumers by removing the effects of temperature when purchasing gasoline."


This seems to address the uniformity of price vs. amount of "energy" delivered into your tank.

However, will your scanguage measure different in the winter (gas remains cold) vs. the summer when the gas will warm up and expand in YOUR tank?

I'm glad that I don't obsess on this topic (I have plenty of other stuff to obsess over)!

 

[Pop_Rivit]

Around here the pumps are deep underground. The temperature is within a few degrees year round, despite the surface temperature.

While the fuel in the pump may expand or contract slightly, it's a small amount compared to the total amount you may pump, most of which comes from the tank that is at a consistent temperature.

 

[javacontour]

Quoted for truth.

In ground tanks largely address the concerns about volume expressed here.

I believe the fill in the AM or after sundown is more about evaporative emissions concerns. Trying to keep the levels down so an area doesn't have to experience even more EPA controls due to the number of days below some EPA air quality measure.

Originally Posted By: Pop_Rivit
Around here the pumps are deep underground. The temperature is within a few degrees year round, despite the surface temperature.

While the fuel in the pump may expand or contract slightly, it's a small amount compared to the total amount you may pump, most of which comes from the tank that is at a consistent temperature.

 

[Quattro Pete]

Originally Posted By: doitmyself
This seems to address the uniformity of price vs. amount of "energy" delivered into your tank.

However, will your scanguage measure different in the winter (gas remains cold) vs. the summer when the gas will warm up and expand in YOUR tank?

And an add-on question: what does the scangauge actually measure? Injector pulses? If so, it probably measures volume as well, but depending on the temperature of the fuel in your tank, that volume may represent different amount of energy delivered, so this in itself will introduce some error. Although if the same volume has more energy, then I guess the number of injector pulses will decrease, so the reading may still be accurate.

There are so many variables that can affect MPG that I would just not worry about all this.

 

[Patman]

Even when the underground tanks are keeping the fuel at roughly the same temperature, I also worry about how the temperature variation is affecting how much fuel is in my tank, which will also affect how I'm calculating my MPG from one tank to the next. With all these things that hinder accurate MPG calculation, it's enough to drive me crazy that's for sure!

 

[doitmyself]

Originally Posted By: Pop_Rivit
Around here the pumps are deep underground. The temperature is within a few degrees year round, despite the surface temperature.

While the fuel in the pump may expand or contract slightly, it's a small amount compared to the total amount you may pump, most of which comes from the tank that is at a consistent temperature.


This "hot gas" issue stirs up a hornets nest of controversy.

While the underground tank temps. remain stable, most arguments imply that the stored gas temp doesn't change much during it's brief stay at a well used station. I think this is what the controversy is about? Down south, gas may be delivered at 80F (it doesn't change much underground) while in Canada it's delivered at 60F. In one scenario the customer makes out good, in the other, the seller makes out.

Here's one site showing the "point/counterpoint" arguments:
http://www.theoildrum.com/node/2787

I haven't studied this stuff much, but on a huge scale, there might be something to consider here, if we could only determine what facts are correct. For a single vehicle, I don't know?

I have observed one thing. At my workplace, if our 550 gallon gas tank is filled too high, within a day the gas expands and leaks/pours out of the overflow quite bad (no numbers to quantify).

 

[MolaKule]

Quote:
While the fuel in the pump may expand or contract slightly, it's a small amount compared to the total amount you may pump, most of which comes from the tank that is at a consistent temperature.


Very true. The percentage change would miniscule.

I would say that unless you run a vehicle inside on a dynomometer, there is no way you can remove all the variables that would affect mpg.

 

[Duffman77]

Originally Posted By: doitmyself
Originally Posted By: Pop_Rivit
Around here the pumps are deep underground. The temperature is within a few degrees year round, despite the surface temperature.

While the fuel in the pump may expand or contract slightly, it's a small amount compared to the total amount you may pump, most of which comes from the tank that is at a consistent temperature.


This "hot gas" issue stirs up a hornets nest of controversy.

While the underground tank temps. remain stable, most arguments imply that the stored gas temp doesn't change much during it's brief stay at a well used station. I think this is what the controversy is about? Down south, gas may be delivered at 80F (it doesn't change much underground) while in Canada it's delivered at 60F. In one scenario the customer makes out good, in the other, the seller makes out.

Here's one site showing the "point/counterpoint" arguments:
http://www.theoildrum.com/node/2787

I haven't studied this stuff much, but on a huge scale, there might be something to consider here, if we could only determine what facts are correct. For a single vehicle, I don't know?

I have observed one thing. At my workplace, if our 550 gallon gas tank is filled too high, within a day the gas expands and leaks/pours out of the overflow quite bad (no numbers to quantify).


I remember whatching a show (might have been W5, cant remember) that was covering calibration of this device, there were a few out of calibration of what they tested. One thing that they did note though was that the average Canadian temperature is below the calibrated temperature so the vendor comes out ahead more than the consumer on average.

 

[Shannow]

I would imagine that if the gas in the fuel rails were hotter, it would be a little less dense, and viscous, so for a constant fuel pump pressure and injector pulse width would probaby deliver pretty much the same mass.

Where the service stations lose out here is that the tankers are hot when theyn deliver, and the fuel quickly reaches ground temp and loses salable volume. Fuel companies refuse to compensate for it (they also won't deliver if vapour recovery systems are installed on tank vents.

 

[mechtech2]

Cold gas is more dense. Just a little, but in that direction, for sure.

The old Shell mileage runs always had guys filling up in the morning, for the cooler gas. They are talking tenths and hundredths MPG, though.

 

[Vikas]

scangauge measures nothing as far as actual fuel consumption is concerned. It infers fuel consumption by measuring the air intake via MAF (or via MAP) and then "assumes" that engine is running at 14.7 ratio and computes the fuel.

The injector pulse width is NOT a standard OBD-II parameters and thus scangauge does NOT have access to it.

- Vikas

 

[lenjack]

Inconsequential difference.