2017 Biggest MPG Overachievers: EPA Highway Rating vs Real-World Testing

“Your mileage may vary” is one of the oldest proverbs in the automotive rulebook. But even though the EPA is constantly looking for ways to improve its testing procedures and rating calculations, “YMMV” still applies to today’s EPA fuel-economy ratings—fueleconomy.gov even has an entire section titled “Your Mileage Will Still Vary.” So we devised our own test procedure in an attempt to better replicate how most people drive on the highway, beyond the constraints and complicated math of the government tests. Our test entails a 200-mile out-and-back loop on Michigan’s I-94. Drivers are instructed to maintain a GPS-verified 75 mph, using the cruise control as much as possible, and to run the air conditioning at 72 degrees if the vehicle has automatic climate control or at a moderate setting if it does not.

After testing more than 100 vehicles through December 2016, we tabulated the results to find the outliers. Here are the biggest overachievers, ranked in order of percentage difference between our real-world test result and the EPA-rated highway mpg number. To see the biggest underachievers, check out this list.

EPA highway rating: 29 mpg

Model tested: 2.0L turbocharged flat-four, seven-speed dual-clutch automatic, RWD

Porsche’s decision to install turbocharged flat-four engines in its mid-engined Boxster and Cayman sports cars was the subject of much controversy. It was ostensibly a play to increase fuel economy, but the EPA numbers for these new powertrains for the most part did not show an improvement over the old flat-sixes. Those numbers proved to be conservative compared with our results, however, given that several Boxster and Cayman variants appear on this list of overachievers. The base-level 718 Boxster, with its 2.0-liter flat-four mated to a seven-speed PDK dual-clutch automatic, beat its EPA rating by 4 mpg in our test. READ MORE>>

EPA highway rating: 28 mpg

Model tested: 2.5L turbocharged flat-four, seven-speed dual-clutch automatic, RWD

Although this Cayman S uses a larger and more powerful flat-four compared with the standard 718 Cayman and Boxster, its 350-hp 2.5-liter engine still overdelivered efficiency-wise. Mated to a seven-speed dual-clutch gearbox, the hardtop Cayman S with its 2.5-liter flat-four recorded an impressive 32 mpg in our test, besting the EPA result by 14 percent. It was also only 1 mpg behind the base Boxster's result, showing that the extra power and displacement don’t exact a big fuel-economy penalty when you’re cruising at highway speeds. READ MORE>>

EPA highway rating: 26 mpg

15 percent difference
Model tested: 3.0L turbocharged V-6, eight-speed automatic, 4WD

For a full-size luxury sedan that went from zero to 60 mph in 5.0 seconds in our testing, 30 mpg on the highway is nothing to sneeze at. Cadillac’s top-dog sedan, the CT6, earned that number in its most powerful form, too, with a 3.0-liter twin-turbo V-6 making 400 horsepower and driving all four wheels. The less powerful, 335-hp version of the CT6 couldn’t even match that result with its 3.6-liter naturally aspirated V-6; that model achieved 28 mpg in our testing, beating the EPA by only 1 mpg. READ MORE>>

EPA highway rating: 26 mpg

Model tested: 2.5L turbocharged flat-four, six-speed manual, RWD

Like the Cayman S earlier on this list, this closely related 718 Boxster S droptop beat out its EPA rating by 4 mpg. It has the same 2.5-liter turbocharged flat-four but was mated to a traditional six-speed manual rather than that Cayman’s seven-speed PDK dual-clutch gearbox. Road-trippers will not only appreciate the 30 mpg that’s achievable at highway speeds, but also the relative wealth of cargo space afforded by the Boxster’s front and rear trunks. READ MORE>>

EPA highway rating: 24 mpg

Model tested: Reserve, 3.0L turbocharged V-6, six-speed automatic, 4WD

“Quiet Luxury” is the tagline for the new Lincoln Continental luxury sedan, but maybe Lincoln should start emphasizing the big four-door’s fuel efficiency as well. Our test of the 400-hp Conti, which uses a 3.0-liter twin-turbo V-6 mated to a six-speed automatic transmission, revealed surprising efficiency at cruising speed, with the four-wheel-drive two-ton sedan returning 28 mpg in our hands. READ MORE>>

EPA highway rating: 30 mpg

Model tested: XSE, 3.5L V-6, six-speed automatic, FWD

Toyota’s ubiquitous 3.5-liter V-6 is not the most technically advanced engine, and it pairs with a pedestrian six-speed automatic in the 2017 Camry while many competitors have rolled out eight- and nine-speed transmissions. And yet, relatively old-school tech seems to work well for this top seller, as it bested its EPA result by 5 mpg in our test. A Honda Accord V-6 matched that figure in our highway test, but the EPA rates the Honda at 33 mpg highway, so it isn’t as much of an overachiever as the Camry. READ MORE>>

EPA highway rating: 26 mpg

Model tested: F Sport, 3.5L V-6, eight-speed automatic, 4WD

Using a similar 3.5-liter V-6 as the Camry on this list, Lexus’s popular crossover SUV also beats its EPA numbers in the real world, at 31 mpg. That kind of result makes us question the existence of the RX450h. That hybrid model achieved the exact same 31 mpg in our highway test (to be fair, the hybrid also beat its EPA number, by 3 mpg). READ MORE>>

EPA highway rating: 31 mpg

Model tested: Quattro S-line, 2.0L turbocharged inline-four, seven-speed dual-clutch automatic, 4WD

Who needs the new fuel-economy-minded Ultra version of the Audi A4 when the standard car achieves such high-mpg results on its own? Even with 252 horsepower and Quattro all-wheel drive, the A4 managed 37 mpg in our test, putting it on a level with several less powerful and less luxurious economy cars. Of course, we've yet to test an A4 Ultra, so it remains to be seen whether it's an overachiever as well. READ MORE>>

EPA highway rating: 34 mpg

Model tested: 2.0L turbocharged inline-four, eight-speed automatic, RWD

BMW's new four-cylinder is an overachiever in more than just fuel economy; beyond topping 40 mpg in our test, it also propelled the 330i to 60 mph in a fleet 5.4 seconds. Those are impressive results for a 2.0-liter turbo four-cylinder that pumps out only 248 horsepower and 258 lb-ft of torque—at least on paper (many suspect that BMW underrates its engines at the crank). READ MORE>>