When it’s time to top-off the tank, drivers are confronted with a dizzying variety of choices at the pump. There’s premium gasoline, mid-grade, regular and – depending on where you live – some even offer ultra-high octane, with a rating of 94 or above.
Octane numbers, ethanol content and diesel get thrown in the mix, while TV commercials shout about special cleaning additives and better fuel economy. What’s a motorist to do? Is premium fuel worth the extra cost over regular? It’s more expensive so it must be better, right?
Wrong. And this is a common misconception. A lot of people seem to think higher octane gasoline will deliver better performance and economy. In many instances this is simply not the case. In fact, it’s mostly a waste of money. High-test fuel is typically priced anywhere from 20 to 40 cents more than regular-grade gas.
“Use what’s in the owner’s manual. Don’t use more, don’t use less” said Bill Studzinski, Fuels Technical Specialist at General Motors. He also said drivers “should not run the octane above what’s required in their vehicle,” because there is no real benefit.
The overwhelming majority of GM vehicles are built to run on regular-grade gasoline. Some of the company’s high-performance models like the Cadillac CTS-V and Corvette ZR1 are designed to take advantage of the additional octane found in premium fuel.
“If it says ‘premium required’ I strongly suggest using the premium gasoline,” Studzinski said. However, if a driver mistakenly puts 87-octane regular in a vehicle that needs 91 or more, the engine-control computer should be able to adjust spark timing and other variables to prevent damage. “In general, the knock sensors are pretty good,” he said, but drivers will likely experience a drop in performance and fuel economy.
Studzinski strongly discourages the use of other fuel products, though. “Say ‘NO’ to aftermarket octane boosters and organometallic octane-boosting additives such as MMT [methylcyclopentadienyl manganese tricarbonyl].”
“We don’t recommend using any of those,” he said because they can plug up catalytic converters, a critical and expensive-to-replace component of a vehicle’s emissions-control system. Thankfully these sorts of additives are not used in gasoline sold in the United States and Canada.
Studzinski also warned drivers to steer clear of high-octane race fuels (like those with a rating of 100) sold at some gas stations. These products can contain high amounts of ethanol or methanol and are “really not advisable” for street-driven vehicles.
Stephen Russ, Technical Leader with Ford Motor Company Engine Engineering echoed much of what his cross-town colleague had to say. If a driver runs premium fuel in a vehicle that only requires regular he said, “typically it would not be noticeable.” But there could be slight benefits in certain situations such as hot, dry weather or while towing.
In the past it was thought running premium fuel when only regular was called for could cause damage. “Most every engine, every manufacturer, can handle that higher octane so there are no deposit concerns,” Russ said. And according to Studzinski, “going up in octane is ok for the vehicle, it doesn’t damage it.”
“Under high-load conditions the additional spark advance from the premium fuel will result in higher cylinder pressures, but they are limited by the [computer] calibration to what the engine structure can handle,” Russ said, so there’s no risk of damage from running higher octane.
Occasionally, manufacturers will list specific benefits to running premium fuel. For instance, when equipped with the optional 3.8-liter V6 engine the 2013 Hyundai Genesis Coupe is rated at 344 horsepower on regular gasoline and 348 on premium. Pick your price, pick your pump and pick your performance.
Still, when it’s time to fill ‘er up most Americans go for the cheapest option. According to Studzinski “about 80 percent of the gasoline sold in the United States is regular unleaded,” that’s an estimated 140 billion gallons per year.
At the end of the road it’s a driver’s choice whether they up the octane and buy premium fuel, but experts say go by the book. “We defer to the manufacturers” said Carlton Carroll, a spokesman for the American Petroleum Institute. He also said “these are the people that have designed and built the car and they know the type of fuel required.”