Won't Get Fueled Again: AAA Testing Suggests Premium Gas, for the Most Part, Isn't Worth Your Cash
Most readers of this site know exactly what an octane rating is and how it relates to the bang it provides in an engine. Hauling up to the pumps and being presented with a choice of everything from 87 to race gas is one of the benefits of living in America.
Higher octane fuel is more expensive than other grades and the gulf between regular and super-duper-extra premium is steadily increasing. Is it worth “treating” your car to a tank of high octane every now and then? The American Automobile Association says absolutely not — and they have the testing to back it up.
For its tests, AAA used 87-octane (regular) and 93-octane (premium) gasoline in six vehicle models varying in body style, size, type of fuel delivery system and air induction system. Each vehicle was identified as a model that the manufacturer recommends the use of premium gasoline. All gasoline used for testing was EPA Tier III certification fuel with 10 percent ethanol content in both regular and premium octanes. Certified test fuel was used to remove variability in fuel quality and additives. Each vehicle was tested on a dynamometer.
The organization does allow that premium gasoline provides a benefit in select vehicles. Vehicles such as high-strung supercars need the extra octane in order to run optimally and produce the advertised amount of horses.
“AAA’s testing reveals that drivers could see modest gains in fuel economy and performance when opting for premium gasoline in vehicles that recommend, but do not require, the higher-octane fuel,” said Megan McKernan, manager of the Automobile Club of Southern California’s Automotive Research Center. “Those seeking the maximum capabilities of their performance-focused or utility vehicle may see some benefit from using premium gasoline, particularly over the long haul.”
Makes sense. Only the most tinfoil-hatted paranoid android would believe a random engineer deep within the bowels of an OEM would slap a “Premium Recommended” sticker on a car simply because they’re getting kickbacks from Big Oil. To prove a point (and settle many arguments fought in garages since the invention of premium unleaded), AAA strapped test gear to a few cars and came up with some quantifiable results.
In a fit of real-world usability, the association published the exact make and models they used in the test, along with exacting results. From the report:
- Fuel economy for test vehicles averaged a 2.7 percent improvement. Individual vehicle test result averages ranged from a decrease of 1 percent (2016 Audi A3) to an improvement of 7.1 percent (2016 Cadillac Escalade).
- Horsepower for test vehicles averaged an increase of 1.4 percent. Individual vehicle test result averages ranged from a decrease of 0.3 percent (2016 Jeep Renegade) to an improvement of 3.2 percent (2017 Ford Mustang).
- According to national averages, the price difference between regular and premium gasoline is approximately 20 to 25 percent, or 50 cents per gallon.
- The modest fuel economy improvements found in AAA tests do not offset the higher cost of premium gasoline.
The 7.1 increase increase in the Escalade is interesting, until one remembers their learnings in basic math. At 15 mpg, that percentage increase works out to a single mile per gallon. In the A3 cited in the story, a 1.0 percent drop in economy would bring a 28 mpg performance down by approximately a quarter of a mile per gallon.
Those numbers are averages of results taken while testing those machines on four different simulated road gradients. The Caddy recorded its biggest increase in economy on flat terrain at 65 mph, jumping from 23.3 mpg to 26.4 mpg. This points to the cylinder deactivation technology benefitting greatly from the good stuff. A 6-percent grade at 55 mph saw an increase from 10.73 mpg to 11.02 mpg. The other testing parameters were a 2-percent and 4-percent hill taken at 65 mph.
Horsepower results are even more interesting. The study cites usage of a naturally aspirated 2017 Mustang equipped with the 5.0-liter V8 and an automatic transmission. Ford rates this engine at 435 crank horsepower, noting “premium fuel” in parenthesis. Check out AAA’s dyno results:
The organization used six vehicles in its testing: a rear-wheel drive 2017 Ford F-150 with the 3.5-liter EcoBoost and 10-speed automatic, a Cadillac Escalade equipped with its fabulous 6.2-liter V8 and eight-speed auto, a stickshift 2015 Mazda Miata, a non-quattro Audi A3 with the six-speed dual clutch autobox, a 5.0-liter Ford Mustang automatic, and a row-your-own MultiAir-equipped Jeep Renegade.
The full report, all 68 pages of it, can be found here.
Tele Vision on Dec 16, 2017
My CTS-V requires premium so that's what I feed it. The Ford truck and the Equinox don't so they run regular gas. Weirdly, many people still think that premium fuel has more power per unit and will do stupid things like fill up with premium before a cold snap or a long road trip. Regular gas has more 'bang' than premium gas: octane being a 'bang-inhibitor' that allows for higher compression like that in my Cadillac. A lower-compression engine simply doesn't require that much octane so using the more expensive gasoline - that results in a loss of power and poorer fuel economy - instantly puts you upside down in financial terms. Just this past Summer a friend was complaining about his Kawasaki Mule not running as well as it used to. It turns out that he'd filled it with premium fuel a few months earlier as, in his mind, some kind of a favour to it. The lack of performance was noticeable with three big guys in it.
Tankinbeans on Dec 16, 2017
I think I read that each grade fuel tested for this comparison was E10 indicating 10 percent ethanol. Any fuel with ethanol is less energy dense than fuel without ethanol, if I understand the chemistry correctly. It follows that all things being equal if both grades have the same energy density, and the timing voodoo isn't required, then on a strictly fuel economy/cost basis E10 87 is preferred. However, in my state certain brands off E0 91 at about $0.50 more than E10 87 (mid-grade has been bumper up to E15 88). On E10 87 my combined mileage in the 2017 Mazda6 - with 13:1 compression - is 28 (I don't break it down city versus highway because I never have a tank that's 100 percent one or the other), but with E0 91 my combined mileage is usually 33-35. I top up at half tank and have recorded each fill in fuelly with notes regarding grade. Am I understanding the chemistry correctly in that E10 is less energy dense than E0, or is there something else at play?
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