Gas Slips or on board computer?

My take is since I can't even visually measure the gas that went in the tank, and have to rely on some computer to do the analysis for me, should I rely on the computer that served the gas, or the computer that received and is burning the gas? In the Prius' case, I tend to trust it more than the gas pump which is known to have issues.

It's worth reposting this link that was posted in the thread earlier -- it's interesting reading:

http://www.users.qwest.net/~taaaz/AZgas.html

Summary above the above link:: Due to temperature, the volume of gas you pump may not be the amount of gas you pay for. Strategy: Fill up when it's cold.

Quotes:

"Gasoline volume changes approximately 0.125% for every 1ºC change in temperature (0.058%/ºF) . The energy content of a gallon of gasoline purchased by a motorist in Nome, Alaska in January could, theoretically, be as much as 8-10% greater that that of a gallon of gasoline purchased by a motorist in Phoenix, Arizona in July."

and

"The temperature-induced inaccuracy in this example exceeds by a factor of 4.5 the permissible dispenser inaccuracy."

and

"Depending on the manufacturer, a single hose dispenser delivering 3 grades of gasoline has from 0.5 to 0.75 gallons of residual motor fuel contained in the hose from the pump to the nozzle of the dispenser. ... The range in residual volume amounts to 3.7 - 5.6% of a 13.401 gallon purchase."


--foo

 

<div class='quotetop'>QUOTE(Rufaro @ Jul 16 2006, 11:12 PM) [snapback]287447[/snapback]</div>

Yes, there is. You look at the notes you take after each fill up.

After every fill up, I record (1)MFD MPG, (2)MFD/Odo trip meter miles traveled after fillup, (3)Odometer reading, (4) $/gal, and (5)gals pumped. Not that anal, but it only takes a minute to record the data.

 

<div class='quotetop'>QUOTE(seattlite @ Jul 17 2006, 12:34 AM) [snapback]287459[/snapback]</div>

I KNEW there was some newfangled mathod....

 

<div class='quotetop'>QUOTE(seattlite @ Jul 17 2006, 03:34 AM) [snapback]287459[/snapback]</div>

That's exactly what I do. Then I plug the numbers into a spreadsheet.

After 7 fillups, I'm averaging 49.2 calculated and 49.8 MFD. The difference is about 1%, close enough for me.

Of the 7 fillups, MFD was higher 4 times, MFD was lower 2 times, and one time was a tie.

 

I trust the on board Fuel Injector detectors more. Here is something I've posted before on this same topic:

Don't put too much stock in the gas pump's meter figure. I would trust the car first. Read this article form the Seattle Post-Intelligencer:

http://seattlepi.nwsource.com/local/264462_gaspumps27.html

Here is the same article discussed on NPR:

http://www.npr.org/templates/story/story.php?storyId=5304258

According to the article, a pump can be up to 1% inaccurate and still pass inspection. Even with that margin of error 80% of gas stations had some failure in the 3 year time period of the study.

Here is something interesting they discovered: If you want to get the most gas possible in your tank, pump as slowly as you can. The pumps errs in your favor at that speed.

 

All three ways, slips (calculating current fill vs current driven), spreadsheet (previous fill vs current driven), and MFD. The gas pump I usually go to lets me dribble in gas and not click off.

 

Now, the 2006 MFD only has the one option for displaying the MPG, right? I haven't filled up yet (my baby is one week old yesterday), but things I'm reading about the 2006 is that the MFD resets after you fill up, but some 2006s say they don't. I wish they allowed the MFD to show lifetime MPG based on the total ODO reading and at least one trip MPG. I like having that instant feedback and being able to see what my commute MPG is on the MFD, but figure that I'll have to track the lifetime the old fashioned way.