Gas Mileage: Whom Do You Trust?

Then you won't want to read this.

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Accuracy at the pump Rising gas costs aren't the only problem for consumers. They could pay too much just because they are tricked by the pump.

By KELBY HARTSON CARR

Date published: 5/31/2001

[...]

David Lazier, chief of the California division that oversees gas pumps, said an investigation there led to about 30 stations being busted for duping customers. Investigators in other states have unearthed similar fraud.

In California, some stations were using equipment that tricked customers into believing they were getting more gasoline.

"We do have a certain faction that feels they need to make an illicit profit," he said.

The gas dealers were especially difficult to catch there because the equipment initially fooled inspectors. While inspectors usually pump 1,

5 or 10 gallons of gasoline for testing, the illegal equipment ensured those amounts dispensed properly.

"They were using our own test methods to beat us at our own games," he said. "We started receiving enough complaints to lead us to believe something was going on."

When undercover inspectors pumped differing amounts of gasoline--such as

6 or 9 gallons--they discovered they were shortchanged by as much as a third.

He said savvy consumers can watch for such a scam.

For example, if a gas pump is rigged, the gauge that shows gallon measurements will speed up right after the 1-, 5- and 10-gallon marks, and go really slowly as they approach those points.

"You could actually see that speed up and slow down," he said.

He also said consumers should track their gas mileage and be concerned if it suddenly plummets.

"If you notice all of a sudden you're getting a lot less miles per gallon, that's usually an indicator," he said. "It could be a lower octane fuel. It could be you're not getting everything you pay for."

[...]
Reply to
richard schumacher
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Today I drove about 160 miles, much of it at 70-80 mph with the AC on. My mpg dropped to about 50.

Al

Reply to
A Sherman

Wow! Nice tailwind.

Reply to
Bill

Davoud:

richard schumacher:

"This industry is very highly regulated." ""It's not a regular practice that we find. I've never seen anyone tampering."

My point is that tampering is rare.

30 stations in California? Out of how many thousands? My point is that tampering is rare.

Davoud

Reply to
Davoud

I would trust the display. It's tied to the very prcise fuel metering system that sends gas to the injectors. You have a big discrepency that may be attributable to some filling errors - e.g.: early pump shut off, car not level when filling, fuel coming from warm storage tanks.

While it doesn't make a noticable difference in a car that gets 50 mpg, it is worth noting that you burn fuel by weight, not volume.

Reply to
Curtis CCR

Well, my 92K mile experience would differ. While there are variabilities in individual fillups, over the span of 3 years where I logged each of 203 fillups and the number of miles between them and found that the MPG display in the Prius was 5.21% higher than the calculated MPG. It was pretty consistent; a few times higher and a few times lower. I have to believe that over 203 tankfulls at all sorts of gas stations, that the errors due to top offs, temperature changes, pump accuracy etc. should be pretty much netted out. At the end of the day, the true cost of fuel for the car is what I actually pay for it and pump into the car, and not what the meter in the car might tell me. Dividing that by the number of miles I drove as shown on the odometer will yield the true MPG.

Curtis CCR wrote:

Reply to
PriusGeek

Yes, the true cost of the fuel depends on what you pay at the pump - which has nothing whatsoever to do with the original question.

Everyone has their own opinion. After posting my pump tracking spreadsheet in the PriusChat forums, John1701 (a well-known Prius blogger) challenged that the only true measurement of MPG is the hand-calculated method, not the MFD, and suggested I view his 114k+ miles of records. I did so, plugged them into my own spreadsheet, and found out that his lifetime MPG were less than 2mpg off from hand to MFD.

While some Prius geeks (not talking about you, PriusGeek!) track fuel, mileage, cost, and MFD readings, I also happen to track fuel pips on the "guess" gauge. For the most part, the first pip disappeared after anywhere from 110-160 miles, and all the rest dropped after 20-60 miles. The one time I got GREAT mileage for me (56), the first pip dropped at 50, and the next tank showed crappy mileage (36). Translation: I didn't fill up all the way prior to the great mileage. Amazingly, my MFD said both tanks were about the same as far as MPG. You guys can debate this all day, talking about teh 9/10 of a cent issue, the fuel injector issue, the gas pump issue, and the "I know I filled it all the way up, even though I'm at a different gas station using a different model of pump. The only constant in this is the Prius and its MFD, so that's what I'm going with. Somehow, I think it's slightly more accurate than a commercial gas pump or any driver on the road, but then, I tend to trust computers. They're pretty good at that cipherin' stuff...

Reply to
Miwaku

Right. Your readings and calculations are valid for your car. Isn't there a site where a wide range of such readings and calculations have been posted? Damned analog devices. Hard to get consistency in mass production.

Reply to
Bill

No, not an analog issue (except for the fill-ups).

How come PriusGeek reports a 5.2% difference and I get about 3% for the same calculation? I have a 2005. Is the "classic Prius" different?

Does anyone know exactly how the MPG display is calculated? Is it the calculation of the total fuel through the injectors divided by the distance covered, or some kind of a weighted average?

Al

Reply to
A Sherman

I'm sure that individual driving styles as well as differences between vehicles (tire wear, brakes, etc.) accounts for some of the differences. I keep the same data on my '06, and over 16 tanks, my variance is 2.7% (display more optimistic than the calculated value) But that's not the whole story, as I have several tankfulls where the variance was as much as +/- 10%, so it is important to look at the data over a significant number of fillups.

On the other hand, my 02 Classic was the best car I ever owned until I bought my 06! For more perspective I get infinite pleasure filling up with 10 gallons after 500 miles of travel while the Hummer next to me is maxing out his credit card after a couple of hundred miles.

A Sherman wrote:

Reply to
PriusGeek

Yes, it's called GreenHybrid.com. Currently there are 2,379 cars in the mileage database, and the majority of them (773) are Prius II's. Each user can decide if they want to record by hand or MFD.

Reply to
Miwaku

That's the analog part Al. Open the injector and some fuel squirts in. How much? Well, that depends on fuel pump pressure and how long the injector is open. Yes, you can count the times you open the injector and go digital all the way to the display, but the part that counts (pun intended) is analog.

Reply to
Bill

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