Guess What? Your Dash MPG Readout Is Probably Just A Pipedream

Digital miles-per-gallon readouts, a feature now standard on nearly all new cars as of the 2013 model year, appear to give drivers an accurate look at real-world fuel efficiency, but may differ greatly from Environmental Protection Agency mpg estimates on window stickers.

The accuracy of those dashboard readouts varies greatly by make and model and in some instances may give drivers the wrong impression about how their driving habits impact fuel consumption.

“I don’t think anyone is trying to hoodwink anybody,” said Dan Edmunds, director of vehicle testing for automotive research firm Edmunds.com. “But these meters have never been 100 percent accurate. They are more for instantaneous feedback to let you know how you’re doing.”

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TheSteve - 9/16/2013 2:55:01 PM

+1 Boost

No kidding. I drive a BMW. I know.

Real-time MPG, or even MPG over a distance (since hitting the reset button) requires little more than an accurate fuel-flow meter, accurate odometer, some simple math, and a display.

I can tell you that car odometers and speedometers are notoriously inaccurate (speedos err by showing high, while odos usually show low). I can't speak for their fuel-flow metering.

NeoReaper - 9/16/2013 5:34:03 PM

+2 Boost

I've been driving for about 10 years and I've always found the readouts fairly accurate. cars I've driven would range from Audi to BMW to Infiniti. I never paid attention to instant/realtime MPG as that is just the guess-timate based on throttle position, but my trip average MPG has always been accurate enough (within 1 to 2 MPG)

DieselRules - 9/17/2013 12:09:16 AM

+1 Boost

I've put over a half million miles between a '98 Beetle TDI, 2000 A6 sedan manual, 2001 A6 wagon tiptronic, and 2009 Jetta TDI/DSG wagon. The VW & Audi computers have been pretty much dead-on.
On business trips and vacations I've rented mostly GMs (Impalas and Malibus) with some others (Crown Vic, Maxima, Fusion) thrown in. The Fords were good, but I didn't check them as close as the VW products. The GM is so far off you may as well not have a fuel guage in those cars! I was nearly stranded the first time that I discovered that driving some place and arriving with 5/8 of a tank doesn't mean you have enough fuel to get back. In fact, you barely have enough to get 1/2 way back! The middle of a GM guage seems to be the "reserve" location, meaning "Start looking for a station now or you'll be walking!"
This severe deficiency has been repeated across a dozen cars of varying model years. Too bad, because otherwise those North American built Chevies are pretty nice cars (And I love that they copied the 1998+ A6 interior exactly for the newer Malibus, so I felt right at home)

85bmw745i - 9/17/2013 1:08:27 AM

+2 Boost

I was just going to say that my Passat TDI has been spot on every time. And your name says it all. Diesel rules!