When fuel's cheap, motorists are willing to pay 20 cents or so more for premium. But as gas prices sneak back up, the mental wrangle begins anew over whether it's OK to burn cheaper, regular-grade gas.
The answer almost always is yes.
"I personally use regular even though my owner's manual says you'll get better performance with premium," says Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company. He's chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council. Gibbs knows gas.
"My wife runs midgrade (89 octane) in her car, and it's a turbocharged engine" meant for 91-octane premium, he says.
Premium Ã¢â‚¬â€ gasoline having an octane rating 91 or higher Ã¢â‚¬â€ is just 12.1% of sales this year, down from 13.5% in 2002, when it was 22 cents a gallon cheaper, and well below the modern high of 20.3% in 1994, when it was 49 cents cheaper, according to industry and government data. Despite the allure of premium, once they abandon it, most motorists don't come back, the data suggest.
For every dime increase in the price, sales of premium gas drop 1%, Bob Johnson, general manager of gasoline and environmental services for the 7-Eleven chain, figures, based on data back to 1998.
The main advantage of premium-grade gas is that it allows automakers to advertise a few more horsepower by designing and tuning engines to take advantage of premium's anti-knock properties. But auto engineers generally agree that if you use regular in a premium engine, the power loss is so slight, most drivers can't tell.
"I go back and forth, and I'm hard-pressed to notice" whether there's regular or premium in the tank, says Jeff Jetter, principal chemist at Honda Research and Development Americas. He drives an Acura designed for premium.
Import brands, especially, use premium fuel to distinguish their upmarket models. Most Toyotas, for instance, are designed to run on regular or midgrade, while the automaker's Lexus luxury brand prefers premium. Same with Honda and its Acura luxury line.
"Generally, the more expensive the vehicle, the higher the expectation for performance and the more the customer is willing to pay for fuel," says Pete Haidos, head of product planning for Nissan in the USA.
Actually, the price debate is nearly worthless. At 20 cents more for premium, pumping 20 gallons of it instead of regular would cost $4 more. Annually, that's a difference of $171 for a vehicle that averages 14 miles per gallon Ã¢â‚¬â€ as some big sport-utility vehicles do Ã¢â‚¬â€ and is driven 12,000 miles a year.
Gasoline retailers and refiners like high-test because it's more profitable than regular-grade gas is. The retailer paid about 8 cents more for the premium you pay 20 cents more for Ã¢â‚¬â€ though that margin can swing wildly. Refiners make a few cents a gallon more on premium than on regular when they sell to wholesale distributors.
As long as it's clean
Profit is meaningless to the modern engine, which, regardless of what's specified in the owner's manual, hardly cares what you use Ã¢â‚¬â€ as long as it's clean.
Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used.
Extreme pressure inside the cylinders causes knock, which is the sound of the pistons literally rattling inside the cylinders. Too much too long can damage the engine. A little now and then won't.
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.
Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.
Automakers say they don't test premium engines on regular to check the difference, but some auto engineers estimate that power declines roughly 5%.
"We can't guarantee the vehicle will perform as specified if other than premium fuel is used," says Mercedes-Benz spokeswoman Michelle Murad. All U.S. Mercedes engines specify premium.
All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.
Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.
High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine.
No data show that engines designed strictly for regular run better or longer on premium.
The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."
There is "no way of taking advantage of premium in a regular-grade car," says Furey.
"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.
"No customer should ever be deluded into thinking there's any value in buying a higher grade of octane than we specify," says Toyota's Paul Williamsen, technical expert and trainer.
But premium retains a mystique.
Even Mayne, the sensible Subaru owner who has switched to regular, says she'll buy premium when her neighborhood station has a special price. "It's my perception that I might get better gas mileage or that it might be better for my engine," she says.
"I would stop driving rather than use a lower grade of gasoline," says Andrew Martschenko of Boston, who drives a 2003 Nissan Maxima. Nissan says premium is "recommended" for that engine Ã¢â‚¬â€ automaker code for regular is OK, but you'll only get the advertised power on premium.
If the price difference between regular and premium grew to $1, Martschenko says, "Then I might consider trading down" to regular.
Guilt plays a part
Some people feel almost guilty, as if they are abusing their cars, when they don't burn premium, says gasoline retailer Jay Ricker, president of Ricker Oil of Anderson, Ind., which operates 28 stations. "They go all the way down to 87 (octane), but maybe every fourth tank they put in the good stuff."
Sam Turner has seen the appeal, too. He's president of Favorite Markets of Dalton, Ga., which operates 139 outlets in three states.
He recalls visiting one of his stations during a price war with a nearby station, which had cut the price of premium to just 4 cents more than regular, instead of the usual 20-cent difference.
"A customer was waiting and asked me if I was going to match the guy across the street. I said, 'Yeah,' and he said, 'Good. For 4 cents, I'm gonna buy super.' "