The "original question" was not an MPG calculation.
The "original question" is "why is the Prius calculated MPG
*consistently* wrong?"Not one time, *consistently* wrong, in ONE DIRECTION.
Not a V-O-L-U-M-E error.
Try a gallon of zero energy content gasoline and estimate the MPG.
I see you don't understand reference to a limiting case. Or the issue.
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To the point, do you see any indication of the OP's observation -- consistent calculated MPG error and directional bias?
That is a contradiction. One gallon of 87 octane is the same volume as 87 E10 and the same volume as 89 octane. The octane does not change what a gallon is.
OTOH, I am not convinced that the gallon count on the pump is accurate. I filled a 5 gallon can with over 5.25 gallons and it already had some gas in it. I strongly suspect that many pumps, verified or not, are charging for inflated gallon figures.
Since January, 2005 I have filled the gas tank exactly 316 times, consuming exactly 2,253.713 gallons of gas, for a total cost of $7,005.11 (please note that I am an engineer, a spread-sheet freak, and I keep every gas purchase slip ? weird!) While I have owned this car, I have driven exactly 110,898.8 miles.
Take out your calculator and divide: 110,898.8 miles by 2,253.73 gallons.
MPG (long-term average) = 49.21 miles per gallon.
I have not averaged the estimated MPG, but I could easily. I suspect that it would be greater than the actual, but not by very much -- a few percent.
I could easily add a column to the spreadsheet that computes the percent difference between the actual and estimated MPG. Maybe I'll do that.
earle
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Is that UK or USA gallon?
Over my first few fills my Prius C is using 5.0litres/100km or about
56mpg (UK gallon)TonyB
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Loath as I am to get involved in newsgroup pissing contests, this seems to be verging into the "How many angels can dance on the head of a pin?" question.
There are many variables in gasoline consumption, including but not limited to how one drives, the weather conditions, traffic flow, whether you fill up (sic) at 2 PM in the summer or 7 AM in the winter, the gasoline blend (E10 is becoming more common year-round in some states, and in winter months in others), the type and size of the tires on the vehicles, etc. I suspect most folks drive their cars to get from here to there, not for a chemistry lesson.
I have two hybrids, and while I find the on-board MPG calculations interesting, I also keep spreadsheets that calculate MPG and $PG based on the data given which is not precise but is good enough for what I want to know, i.e., "How am I doing? Is there something needing attention with my car or with my driving? Are my tires properly inflated, needing rotation or re-balancing or replacement? Is it time to replace the fuel filter? How soon do I need to refuel (that one usually is off to the sooner than later side). Wow now matter which way you drive I-80 across Wyoming, the wind rarely is right behind you."
Even if I knew the chemistry of the fuel - for each and every fill-up, what practical difference would it make to me? I'm not designing an engine or working for a refinery. I'm driving a car. I suspect that most folks in the real world care more about the immediate practical factors than the theoretical, of which even the fuel chemistry is only one component.
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