Vehicle Gas Consumption - Accurate?

They are not. They are indicators, not gauges.

Do the math for yourself to see where yours lies.

And, if your Prius has a bladder tank like my old 2004, you will find that the pressure of the fuel dispenser makes a big difference in how much gas you can get in. My county requires vapor recovery nozzles while neighboring counties do not. I used to get from one half to one gallon more in a fillup when filling up in a neighboring county. That makes it hard to do consistent measurements. My newer 2010 does not have the bladder tank. The bladder tank was an interesting idea, but I am glad they did away with it. One time on a trip with the 2004, the bladder must have folded in such a way, that I could only get 5 gallons into a nearly empty tank. The next fillup was normal and it never happened again.

Pat

You should never, EVER do the measuring across different pumps.

Go to the same pump across fillups, preferably at the same time of day, if you want to have a reasonable presumption of any kind of accuracy.

I have compared one tank so far with my C, and I did not top off either fillup, but did use the same pump.

Dash reading: 52.0 MPG Calculated: 50.9 MPG

Doing my second tank now, and will top off both. Let you know the results next week.

Bob

Check for yourself. I purchased my 2007 last month based on the display mileage (47 on a long test on both city and highway). I just checked it. Display said 44.8, but it was really only 39.8 :( That is combined highway and city. That matches the best highway mileage I ever got on my 98 Corolla, down to about 33 after 240,000 miles on it.

I filled up on the 1st of the month as I wanted to start off the month noting in MS money the gas was toward the prius C. The sent me off wit a full tank from the dealer. My calculations showed that I got 50+ mi per gallon. I will check again next month. Most of my mileage was on Connecticut two lane roads where speeds are typically between 35 and 50 miles per hour. From what I have seen the city rated mileage seem to apply for those speeds. I was very impressed by how the car did one mileage over rolling hills between Granby, CT and Barkhamsted, CT. I did some highway driving at 60 - 70 miles per hour but not a lot.

Danielle

I'm on my 4th Prius, have had at least one of each generation. Anal-retentive personality that I am, I have recorded for each tank the fill-up amount, displayed MPG, outside temperature, cost and calculated the actual MPG. Generally speaking, the Prius displays were all significantly optimistic in the MPG department. Overall, on 25 fills so far on my 2011, actual MPG averages 6.2% less than the MPG on the display.

personality that I am, I have recorded for each tank the fill-up amount, displayed MPG, outside temperature, cost and calculated the actual MPG. Generally speaking, the Prius displays were all significantly optimistic in the MPG department. Overall, on 25 fills so far on my 2011, actual MPG averages 6.2% less than the MPG on the display.

How can they get it that consistently wrong?

How can they get it that consistently wrong?

The volume of fuel injected is measured, energy content not-with-standing. For example, the same volumes of 100% 87 octane gas, 87 octane E10, or 89 octane gas will yield different mileage figures. The manual specifies 87 octane so I suppose it's calibrated to the average energy derived from 87 octane, 100% gasoline. Where I live E10 is mandated by law so I would expect the mileage displayed by my Prius to be higher than my actual mileage.

Fuel chemistry is easily measured and compensated-for, but not in this case, apparently.

Fuel chemistry is easily measured and compensated-for, but not in this case, apparently.

Fuel chemistry in real time? Oh c'mon now. In the lab, perhaps, but not on the road.

So far so good.

Yes...

It's not "calibrated" to anything like that.

WTF?

An injector pulses X amount of gas. X times the number of injector pulses is the total gasoline used. Calculate that against the miles driven in that number of injector pulses.

This is just a fancy engine computer calculated version of the very same thing people do when they calculate their mileage at the pump based on how much gas they put in the tank and how many miles they drove since the last fillup.

The energy content of the fuel is *reflected* in the final calculation, but it is not *part* of the calculation. It used THIS much gas, and drove THAT many miles--period. Lower energy content fuel will deliver fewer miles per volume, regardless of whether you're measuring it at the pump or the engine computer is measuring it at the injector.

Hence the need for fuel chemistry compensation.

not at all.

All we're looking at is the miles per gallon calculation.

Lower energy fuel will deliver fewer miles per gallon. Calculate it any way you like, at the pump or at the injector, it's all the same calculation. Energy per volume unit of fuel is irrelevant to the calculation of how many miles will that volume of fuel take you.

I keep reading on Jalopnik all the bias against hybrids and for diesels, but all they can spew is "miles per gallon". That in and of itself is meaningless when diesel fuel is always more expensive, sometimes significantly so, than gasoline.

Me, let me plug into the computer the unit price I just paid for that fuel--now the computer can tell me the REAL fact I want, which is my fuel price per mile.

And nowhere in this is any need to know or compensate for the fuel chemistry.

Wrong.

yeah, keep telling yourself that.

In the meantime, I will continue to buy specific volumes of fuel at specific prices and have that fuel propel me a specific number of miles down the road, and will be able to calculate (a) my number of miles per gallon, and (b) my fuel price per mile--

--all without knowing OR CARING about the fuel chemistry.

Again, the numbers I calculate will *reflect* the fuel chemistry, but no one needs to know the fuel chemistry in order to calculate those numbers.

Your insistence on calling that "wrong" tells me you're not paying attention.

Read your own drivel and you'll conclude you've impeached yourself.