Volume correction for gas pumps

[Patman]

Most (if not all) gas pumps now list that the volume of gas dispensed is volume corrected (here in Canada it's set to 15 celcius) but I was wondering where that temperature is measured? Is it measured outside at pump level or underneath the ground at tank level?

 

[Loobed]

Probably just before the metering device.

 

[Patman]

Originally Posted By: Loobed
Probably just before the metering device.

But is that device outside or under the ground?

 

[Loobed]

I would say it is outside under all the sheet metal. If it involves metering, than it needs to be easily checked and serviced.

 

[Patman]

I've tried to do a google search but surprisingly not much info is out there. I found something here which indicates the temperature might be taken underground:

http://www.ehow.com/facts_5522133_effect-fuel-temperature-mileage.html

FWIW, the reason why I'm asking is because I want to get the most accurate MPG reading for my Honda, and that would involve filling up my gas tank as close to the volume corrected temperature of 15C as I possibly can. That's because all summer long I was fine tuning the calibration of my Scangauge to the point where I was within a tenth of a MPG of the actual calcluated MPG, but now that the weather is colder my Scangauge has been reading 0.6 to 0.8 MPG too high, which leads me to believe that the only way to truly calibrate it properly is to do it when the amount of gas I'm getting at the gas station is exactly the right amount, and not a corrected amount. And then once it's calibrated, I will always trust the Scangauge to be the most accurate measurement.

 

[carwreck]

From the Wayne website, it looks like it is part of the fuel flow meter in the gas pump.
http://www.wayne.com/index.cfm/go/product-detail/product/automatic-temperature-compensation/
http://www.wayne.com/index.cfm/go/list-products/productline/fuel-dispenser-components/
http://www.ic.gc.ca/eic/site/mc-mc.nsf/eng/lm04344.html
Note: In North America, temperature compensation at the gas pump is only in Canada. US only adjusts for temperature at the wholesale distributor per Wicki.

 

[mechtech2]

But even if the pump is super duper calibrated, the changes that occur in your tank from the pump and ambient conditions will negate this!
Back to square one!

 

[Patman]

Originally Posted By: mechtech2
But even if the pump is super duper calibrated, the changes that occur in your tank from the pump and ambient conditions will negate this!
Back to square one!


True, there are a lot of factors out there which make manual MPG calculations a very tricky effort, but I'm trying to do as many things as I can to make it as accurate as possible. Things such as always filling up at the same station and the same pump (and using the same method of filling the tank-always stopping at the first shutoff of the pump), as well as always filling up when the tank is very close to empty (so that I don't have a big enough volume of fuel left behind that is also expanding or contracting due to temperature)

 

[widman]

Your mileage will suffer in cold weather as the computer or choke will adjust for a richer mixture until the engine gets up to temperature.

The fluctuation in volume is 0.7% per 10 degrees Celsius, so if the temperature drops 10 degrees and there is no compensation, you will see a .14 gallon (18 ounce) difference in 20 gallons.

Here the winds are stronger in the afternoons in winter, so I get a 30 mph tail wind going to the office after lunch. Of course if they start early, I get a 30 mph headwind on my way home to lunch.

And since I live 600 ft lower in altitude than my office, my consumption is 2 mpg higher on the way to work than on the way home if no winds.

Lots of factors at play.

 

[doitmyself]

Patman,

are you doing this just for hobby type interest, or is there a practical reason behind your efforts?

 

[Patman]

Originally Posted By: doitmyself
Patman,

are you doing this just for hobby type interest, or is there a practical reason behind your efforts?


It's just a hobby, but once I get it calibrated this time around I'd like to just leave it alone and not keep messing with it. I've had the Scangauge since July 2011 and should have been done calibrating it a long time ago but I just kept tweaking it trying to get it as precise as possible but had not taken all the factors into consideration like I am now.

 

[Doog]

The Earth's temperature below the frost line (2-4'in most parts of the USA) where gas holding tanks reside is 59*F. So, 60*F is probably accurate.