Vehicle Gas Consumption - Accurate?

Where do you see any mention of W-O-R-K in MILES PER GALLON?

All that is in there is distance and volume. The energy content of the fuel will affect the number of miles traveled, but it has no effect on the measurement of the volume. If the energy content allows the car to go 50 miles per gallon then it will use 100/50=2.0 gallons to go 100 miles. If the energy content is less and the car gets 40 miles per gallon it will take 100/40=2.5 miles per gallon. The energy content affected the amount of work that could be done using a gallon of fuel, but it did not change the volume of a gallon of fuel. And the volume of the fuel is what is included in the mpg calculation. The energy content doesn't even figure into it. If you think it does it is up to you to explain how.

Try a gallon of zero energy content gasoline and estimate the MPG.

I see you have no reasonable explaination.

I see you don't understand reference to a limiting case. Or the issue.

You seem to think if you can't dazzle us with brilliance you can baffle us with bullshit. Try telling us again, a gallon is a measurement of what?

Do you see any mention of energy content in there?

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To the point, do you see any indication of the OP's observation -- consistent calculated MPG error and directional bias?

I see that a measurement is being made and that every measurement can include a calibration error. If the flow rate of the injector is off it is extremely unlikely that it would change size back and forth to any great extent. While the error could go either way it is likely that Toyota would prefer to see higher mpg displayed, so if there must be an error they bias it in that direction and overall you end up with a consistantly high bias in that direction. From what I have experienced the bias is small enough that it is less significant than the error introduced by the shut-off point used to determine when the tank is "full" and the 'at the pump' calculation is made, particularly when dealing with a variable like the air bladder used in the early models.

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.

• I drive an '05 Prius.

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

Is that UK or USA gallon?

Over my first few fills my Prius C is using 5.0litres/100km or about

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.