If you’re filling the tank of your clunker with premium gasoline thinking it’ll give you a bit more oomph or more miles per gallon, stop it.
A gallon of gas is pretty much a gallon of gas. Regular gasoline contains 111,400 British Thermal Units of energy per gallon. Premium gasoline contains 111,400 BTUs per gallon.
The difference between regular and premium gasoline is that the mixture of air in the cheaper gas will explode spontaneously under the higher cylinder pressure of high-performance engines. This premature detonation is what causes the knocking sound. The higher compression ratio allows sports cars and luxury rides to extract more of the power from each gallon of gas.
If your vehicle is designed to run on 87-octane gasoline – and most are – burning gasoline with higher octane will not improve performance. Won’t boost your mpg. Won’t improve your 0-60 mph. Period. Paying more for premium gasoline is an absolute waste of money – again, for most cars.
And it can add up to a pretty big chunk of change. The national average price of premium gasoline is 30 cents a gallon more than regular, according to a recent AAA survey.
So, let’s say you drive a Toyota Corolla and you’re filling up with premium under the mistaken assumption it will give you more power to merge onto the freeway. Each tank costs $3.60 more than it should. If you fill up once a week, you’re spending nearly $200 a year at the pumps, hard-earned money you could be spending inside the Quick Trip on beer, candy and lottery tickets.
The owner’s manual in the glove compartment of some vehicles such as the Volkswagen GTI, Nissan Juke or Buick Regal recommends premium fuel. Don’t bother. Modern automobile engines have sensors that detect engine knocks – uncontrolled burning in the engine cylinder – and adjusts the engine timing.
One caveat: if you’re going to do some heavy-duty driving like pulling a trailer across the Continental Divide, go ahead and spring for a tank of premium.
Some high-performance and luxury cars – BMW, Jaguars, Lexus – require filling up with premium gasoline. Regular gasoline will reduce performance, but often not enough for you to notice. But there are cases in which the reduction in performance may be significant. The editors at Car & Driver recorded 9.8 percent drop in horsepower and 10.1 percent slower times on the test track in a Saab 9-5 with 2.3-liter turbo engine running on regular gasoline.
In a pinch, you can run the occasional tank of regular in a car requiring premium fuel. It won’t ruin the engine.
But if you’re driving a 2012 Ferrari 458 Italia, we’re guessing an extra 30 cents a gallon isn’t a big deal for you.