Answer Man: Are gas pumps really accurate? Who checks them?

Sep 02, 2023

Today's batch of burning questions, my smart-aleck answers and the real deal:

Question: How often is the accuracy of gas pumps checked, and by what agency of the State of North Carolina? I have noticed quite a wide discrepancy in the capacity of my "topped off" tank, as reflected in the amount pumped showing at the pump compared to the tank capacity as stated by the manufacturer. I am an Uber and Lyft driver, so I buy a lot of gas. I have a 2015 Kia Optima Hybrid. The owner's manual states that the gas tank capacity is 17.2 gallons. When I fill my tank, I top off until gasoline almost, but not quite, overflows. At no time do wait until the car is "running on fumes." According to the computerized gauge, I usually get gas when the gauge shows I have about a 40-mile range. With my hybrid car that would mean at least a gallon remaining in the tank. My initial concern regarding the accuracy of the pump began on Sept. 28, when I bought a fill-up at a station in Fletcher. My receipt shows that 19.76 gallons were purchased. That's two and a half gallons more than the Kia specifications would indicate and likely 3.5 more, if you consider that at least one gallon was already in the tank. Over the next couple of weeks, I have noticed a pattern of various other gas stations also producing a reading of more than the gas tank capacity. Could it be that Kia doesn't have the right specs? Maybe the tank really holds 20 gallons?

My answer: I suspect this is the same phenomenon that makes me get up to whiz 30 minutes after my first old-man nightly trip to the bathroom. I think I have some sort of secret reserve tank up by my kidneys.

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Real answer: So the North Carolina Department of Agriculture & Consumer Services is responsible for checking the accuracy of gas pumps statewide. Chad Parker, measurement manager with the Standards Division, helped answer this question, first addressing how they inspect pumps.

"We check the accuracy of each meter annually," Parker said. "Most of the time our inspectors are able to complete their area. Sometimes we do have holes where we are trying to hire a position in this area or that area, but we do our best to check each meter once a year."

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Their data show that calibrations on the meters get rejected at a 3 percent average.

"Note this rate includes both where the meter is giving away too much fuel and where the meter is not giving enough product," Parker said.

The conundrum with the reader's Kia is a tougher nut to crack, and Parker said he could only offer his opinion.

"In my experience we have had many similar complaints, and 90 percent of the time the meters are found to be accurate," he said. "We are testing with a calibrated lab certified prover."

"I just don't know how accurate car specs are," Parker continued. "Plus, you have to account for the tank, the piping/lines, and hoses that feed the engine."

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He did note that gas meters wear over time and may start giving away too much fuel.

Parker said they can have an inspector test specific fuel station meters. Call 919-707-3225 to leave details.

On a personal note, I've had a lot of cars over the years and found the fuel gauge veracity to be a little wacky. But I've also had fill-ups where it seemed like my car took more fuel than it's supposed to hold.

For the reader, I'd recommend getting Kia to verify your tank capacity and your gauge readings.

I'll also note that this reader had kept very meticulous records about his gas purchases.

I'm certainly also open to more reader input on this, and I'm curious to see if a lot of other folks have documented this problem. Shoot me an email if you have.

This is the opinion of John Boyle. Contact him at 828-232-5847 or [email protected]