Does your car recommend you use premium gas? Or if it doesn’t, when you’re pumping your regular gas, do you ever wonder if you would get a boost by paying for high-test? Or have you ever had an old-school car guy tell you that you need to run premium sometimes to clean out your gas tank?
There’s a lot of confusion out there about premium gas, what it’s good for, and who does or doesn’t need it. So, let’s clear things up once and for all.
Why Do Some Cars Use Premium Gas?
Some cars either recommend that you use premium gas or require it. Many cars will have a sticker inside the fuel door that tells you if it recommends or requires premium gas. You can always check your owner’s manual.
So why would you need premium gas? Cars that call for premium gas tend to either have high compression engines or forced induction (supercharging or turbocharging). That means that the fuel and air is under very high pressure in the combustion chamber. That’s one way to make a high-powered engine.
High compression and forced induction introduce their own complications. High pressure (along with heat building up in the engine) can cause the gas to combust before it should. That’s called pre-ignition, detonation, or engine knocking. Knocking can cause damage to engine components, especially if it recurs over a long time. You can recognize knocking as a metal-on-metal “pinging” sound under the hood.
You may have noticed the different octane ratings on the fuel pump: usually numbers like 87 for regular, 89 for mid-grade, and 92 (or thereabouts) for premium. A higher octane rating means that the gas is less likely to pre-ignite.
Which Cars Require Premium?
Now, let’s go back to that note in the owner’s manual or that sticker on the fuel door. Some cars will say premium is recommended; others will say it’s required. Generally, you’ll see it recommended for turbo engine cars like the Ford Fusion and some Audis, or big American V8s like in the Mustang, Challenger, Camaro or Corvette. Edmunds compiled a list of recent models that recommend premium.
Luxury cars like some BMWs and Jaguars, or highly tuned engines like in the Camaro ZL1 or Corvette Z06 are more likely to require premium gas. Again, Edmunds compiled a list of recent cars that require premium gas for you. These engines have the highest risk of knocking. If your car says it requires premium, then you really should use it.
But What If It’s Just Recommended?
So, here’s the thing: modern engines usually have a device called a knock sensor. Just like its name says, it can detect pre-ignition. Your car’s computer can take the information from the knock sensor and adjust fuel and air to prevent knocking.
Manufacturers say the compensation from the knock sensor will reduce power and fuel efficiency. According to How Stuff Works, using regular rather than premium could result in about a half-second slower 0-60 time. Tests by AAA and Consumer Reports don’t seem to bear this out, though.
Consumer Reports tested regular in premium gas in the Acura TLX and Nissan Maxima, both of which recommend premium. They found no significant difference in fuel mileage or 0-60 time between fuels for each car.
AAA performed a similar test on an Audi A3, Cadillac Escalade, Ford F-150, Mustang GT, Jeep Renegade, and a Mazda Miata. They noticed on average fuel mileage was 2.7% better and horsepower was 1.4% greater with premium gas.
Manufacturers contacted by Consumer Reports and AAA noted that the difference might be greater under harsher conditions, like extreme heat or towing.
When you consider the rather modest increase in fuel efficiency, compared to the price difference (which can be up to $0.50 per gallon), you can save money by running regular.
Doesn’t Adding Premium Periodically Clean Out My Engine?
Some people say you should run premium periodically, even if your car calls for regular gas. They claim that the extra detergents and additives in premium fuel will help clean out your engine and prevent carbon deposits. According to Edmunds, premium gas used to have more detergents, but now all grades are basically the same in that regard.
What About Classic Cars?
Gas companies used lead as an anti-knock additive until the 1970s. If you have a classic car, the manufacturer probably designed it with leaded gas in mind. That means it might have knocking with regular gas. That being said, James Dunst, a mechanic and former AAA spokesman, says he’s never seen much problem running classic cars on modern gas:
“I did not hear one complaint about valve problems related to unleaded fuels, either through the event or my shop. As a matter of fact, most classic car owners I talked to said that plug life was longer because of the lack of deposits.”
If you do experience knocking in your classic, you can try higher octane gas. You can also purchase a lead additive, which may help.