The truth about octane: Does it really make a difference if you pump regular or premium?
With the price of regular unleaded gasoline still in the $4-a-gallon range, the comparative price of premium is kind of a bargain at many stations.
When the price of regular surged this spring, the percentage difference between regular and premium at many stations actually narrowed — most likely so drivers will keep buying premium.
Why does that make premium a “bargain”? Well, if $3.19-a-gallon premium was 39% more than regular at $2.29 in October 2020, as reported in Miramar, and premium was at $4.79 in April 2021 — 14% more than the $4.19 price for regular, that makes premium relatively cheaper than before. Woo-hoo. Happy days are here again.
So treat your car to a tankful of premium once in awhile, some mechanics say.
Yeah, yeah, most vehicle manuals say you only need 87 octane unless you drive a luxury or performance car. And plenty of expert sources like AAA and Consumer Reports have long said that you’re wasting your money if you pump premium.
But drivers say they can feel a difference, especially when driving older cars in hot weather. That’s when knocking and pinging get louder and acceleration seems to struggle.
David dos Santos, owner of Japanese Auto Care Specialists in Margate, Florida, says knocking and pinging are a result of carbon and other byproducts left by cheap lower-octane gas, which he says burns less efficiently than higher-octane gas.
He recommends that his customers step up to 93 octane premium every five or six fill-ups, even if their car is designed for 87 octane.
He also advises using a high-quality brand with a level of detergent additives above the minimum standard required. Dos Santos said he only uses Shell or Chevron, but many brands are certified as selling a superior blend approved by car manufacturers called Top Tier. Those gasoline brands are identified at the website toptiergas.com.
Brands that aren’t on Top Tier’s list aren’t selling Top Tier-certified gas, the website says.
Debates over whether cars designed for 87 octane run better when given 89- or 93-octane gas are easy to find on the internet, and 87-octane adherents make strong arguments.
Knocking is caused when fuel in an engine’s cylinder ignites before the piston reaches top dead center. The misfired piston then is thrust toward the back of the crankshaft against the momentum of the engine.
Ignition in modern cars is controlled by the cars’ computers, and those computers are calibrated to detect knocking and advance the ignition timing to eliminate it.
In an undated post, AAA said it found no increase in power or fuel economy when running 93 octane in cars designed for 87 octane. But those tests were conducted with cars that were just two years old.
As cars age, their engines become more susceptible to carbon buildup, also contributing to knocking and pinging by reducing the volume of space in the cylinder, creating heat-retaining “hot spots” that ignite fuel prematurely, changing the fuel-to-air mixture, or impeding regular movement of valves.
Filling up with premium helps clean up that carbon and other byproducts of burning cheaper gas, dos Santos said.
Improvement is real
Experts’ advice notwithstanding, drivers who report feeling better performance when upgrading to high octane gas aren’t imagining things, dos Santos said.
Drivers “will feel more improvement if they drive cars with smaller four-cylinder engines than larger engines,” he said. “But it also improves performance of six- and eight-cylinder cars. Older cars might feel more improvement because they typically have more residue and carbon built up over the years.”
Newer cars benefit, he said. Dos Santos said he treats his car to high-octane, high-detergent gas every two or three fill-ups and the results are noticeable.
Pete Cenzano, owner of Cenzo Car Care in Margate, Fla., said he too uses high octane gas once in a while to help clean out the carbon in his cars. Premium gas gets better gas mileage, he said, which consumers can test for themselves with their tripometers. For some cars, the improved mileage helps offset the higher price for premium gas, he said.
Cenzano says he’ll recommend using high-octane primarily for cars 10 years old and older to address knocking and pinging caused by carbon buildup, and sometimes worsened by gradual deterioration of the cars’ emission systems.
What about pumping regular when manufacturers call for premium?
High gas prices can also tempt those who own vehicles in which high-octane gas is either required or recommended to opt for cheaper 87-octane.
Many of those are performance or luxury cars with highly tuned engines that need that extra octane to run at peak levels. But more and more “ordinary cars and crossover SUVs” require premium, Forbes reported in 2020, “due largely to more widespread use of higher-compression turbocharged engines for the sake of added power without sacrificing fuel economy.”
They include models of Buick Envision, Honda Civic and Chevrolet Malibu with turbocharged engines, and all models of Nissan Maxima, Kia Stinger, MINI Cooper, and Volkswagen Arteon.
Experts say that if a manufacturer merely “recommends” premium fuel for a particular model, then it should be perfectly fine to use regular, as the car’s computer will notice and adjust to the lower octane. But if a driver notices knocking and pinging, then use of higher-octane fuel should be resumed.
If the manufacturer states that premium fuel is required, then drivers should beware of downgrading to regular for any extended length of time. Using regular in a pinch — if, say, there’s no premium gas available — shouldn’t hurt the engine.
But cars that require premium are more likely to knock and ping when fed lower-octane gas. On the highway especially, the misfiring will lead to carbon buildup, Cenzano said.
According to the car enthusiast website Thedrive.com, “this phenomenon isn’t typically harmful to your engine if it happens occasionally, but repeated engine knock can speed up wear and tear.”
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