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Inspection Reveals Variations in Gas-Pump Accuracy


You're listening to ALL THINGS CONSIDERED from NPR News. With gas prices creeping toward the $3 mark a story in today's Seattle Post-Intelligencer Newspaper caught our attention. It turns out that those electronic displays on gas pumps, you know, the ones that keep track of how many gallons you've pumped, well those readings are often in error. The paper reports that since 2002 four out of five Seattle gas stations had at least one pump that failed inspection. Tim Douglas inspects gas pumps for the city of Seattle. I asked him what causes the problems.

Mr. TIM DOUGLAS (Inspector, Seattle Consumer Affairs Weights and Measures Office): Gas pumps are a mechanical device. For all the fancy electronics we see on the outside of the pump, internally there is a mechanical meter that is measuring the fuel. And over time those meters are going to wear. So they will sometimes give more to the customer and other times they will short the customer. I think our statistics show that very slightly the consumer actually benefits most of the time.

NORRIS: So what's the margin of error, what are we talking about? A teaspoon or two or are we actually talking a pint.

Mr. DOUGLAS: No, we're talking about on a five gallon test that we run, and this is standard within the weights and measures community., we do a five gallon test measure. They're allowed an error of six cubic inches, and that translates into something just under a half a cup of gasoline on five gallons. So we're not talking about a whole lot.

NORRIS: Half a cup, but every time you fill up, if you fill up once a week, that can certainly add up over time.

Mr. DOUGLAS: It certainly can especially if your filling the tank in a 20 or 25-gallon tank, that can add up yes.

NORRIS: So you say the margin of error in general is pretty low, but what's the worst case you've ever seen?

Mr. DOUGLAS: I think I've seen like a half-gallon error on a five-gallon test. Now that's pretty extraordinary.

NORRIS: That is, now that is a case where the driver really was shortchanged.

Mr. DOUGLAS: Yeah, yeah. And I've seen it, I think I've seen it once or twice where they were shortchanged. I've seen it several times where the pump has malfunctioned and they were receiving that much extra.

NORRIS: One of the things that I thought was surprising when I read this story in the Seattle Post-Intelligencer was this suggestion that the speed at which you pump the gas can actually affect the accuracy of the meter's reading. What's the story there? What explains that?

Mr. DOUGLAS: I'm not a technician so I can't tell you technically what's going on, but what happens is, and this is what the typical customer does, I know it's what I do, you go in and you hold the handle on the nozzle all the way down so it fills up as fast as you can, or you set it with the little lever on the handle to the fastest speed that it will go. And we find statistically if you do that, the pump is going to deliver slightly less fuel then if you were to set it at the slowest notch that you can set it on the handle. But again it's an amount that is not terribly significant to the customer.

NORRIS: I just wonder what a trip to the gas station would be like with you. What's it like when you pull into the gas station and pump your own gas?

Mr. DOUGLAS: Pump my own gas? Well I'm very aware of all these little factors that I'm looking at as an inspector. So, you know, I'm making sure the pump is on zero and isn't registering anything before I pump. I'm very conscious of the fact if it is going to shut off correctly or not. I may even do my own self-test on the anti-drain valve after I turn it off. I may squeeze it and see if anything comes out or not. So it's sort of like I can't let go of these things when I'm on my own. Drives my wife crazy when we shop.

NORRIS: Well Mr. Douglas it's been a pleasure talking to you. Take care.

Mr. DOUGLAS: Thank you very much.

NORRIS: Tim Douglas is a License and Standards Inspector for the city of Seattle Consumer Affairs Weights and Measures Office. Transcript provided by NPR, Copyright NPR.