Why Your Car’s Gas Gauge Might Be Lying

Man pushing a car that is out of gas
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The next time your car’s gas display indicates you will run out of gas in 20 miles, take the warning with a grain of salt. It turns out that relying on such indicators can get you in a heap of trouble.

According to a AAA study, the accuracy of such systems varies widely. Drivers who rely on such warnings before filling up are taking an “unnecessary risk” that they could run out of gas on the road, AAA says.

To test the systems, AAA joined with the Automobile Club of Southern California’s Automotive Research Center to use a dynamometer — described as “a treadmill for vehicle testing” — to put cars through their paces.

Driving scenarios were simulated to measure the accuracy of fuel economy estimation and range value — “miles-to-empty” — systems.

In a press release, Megan McKernan, manager of the Automotive Research Center, says:

“Collectively, the systems we tested were relatively accurate, but a closer examination of different driving scenarios revealed significant variability based on changes in speed, acceleration and distance.”

When comparing a vehicle’s fuel economy display with the dynamometer, the average error rate was low, at 2.3%. However, some vehicles showed much greater variation, with one vehicle overestimating fuel economy by up to 6.4%, or 2.2 miles per gallon.

AAA says driving style and conditions might account for the lack of accuracy.

The AAA survey found that 74% of drivers use their “miles-to-empty” display to decide when to fill up. Given the test results, AAA recommends another approach: filling up when your gauge falls to a quarter of a tank.

Looking for ways to save on gas? Check out “8 Bad Driving Habits That Are Costing You.”

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