Drivers who pump premium gas into a vehicle that only needs regular may think they’re boosting their car’s performance or keeping the engine cleaner, but unless the automaker requires or recommends premium gas, they’re probably just wasting their money.
Even with low gas prices, premium gas still runs about 60 cents more a gallon than regular, so pumping 10 gallons of premium adds $6 to the bill – but may not provide any benefit.
Is Premium Gas Worth It?
The bottom line: Use premium gas only if it’s required by your carmaker, or if your engine clearly runs better with it. Your owner’s manual will tell you what kind of gas your engine needs.
Which Cars Need Premium Gas?
Typically, performance vehicles have engines that require premium. They usually have high compression ratios, different valve timing, more advanced ignition timing, and higher boost pressure if they’re turbocharged. Years ago, nearly all turbocharged engines needed premium, but some current ones are designed to run on regular.
For engines that need premium, the electronic controls are calibrated so they can take advantage of the added octane and anti-knock capability, and they can produce more power using premium, and get better fuel economy.
But if an engine is designed so that it does not knock on regular fuel, there is no advantage to using premium fuel. Premium won’t change the engineering or the electronic calibrations of the engine. You won’t get noticeably better gas mileage or performance.
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Premium vs. Regular Gas
The primary difference between premium and regular gasoline is the octane rating, a measure of the fuel’s ability to resist “knocking” or “pinging” in the engine. Regular gas has an octane rating of 87, while premium ranges from 91 to 93 (midgrade gas is in between, at 89). You’ll see the numbers on the pump at the gas station.
A “knock” is an early detonation of the fuel in the piston that often sounds like marbles rolling around in a can. It can damage pistons and cylinder walls, so it’s a serious issue. Engine damage like that can be expensive to repair.
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What If My Automaker Recommends Premium Gas but Doesn’t Require It?
For some engines, the manufacturer recommends using premium gasoline for best performance, and the horsepower rating may indeed be slightly higher with premium. In most cases, these engines can still run on regular, though there may be a difference in acceleration and passing response if drivers choose regular.
If the engine starts knocking on regular, switch to premium to prevent damage. Another option is to try midgrade gas to stop the knocking.
Are There Other Benefits of Premium Gas?
Premium grade gasoline used to have more detergent additives than regular that reduced carbon deposits and helped keep engines cleaner, but that changed more than two decades ago when the EPA mandated that all grades of gas have a minimum level of detergents to prevent clogging of fuel injectors. Now, there is no significant difference.
Instead of using premium (or mid-grade), vehicle owners concerned about carbon deposits should buy Top Tier regular gas, which has a higher level of detergent additives than the amount required by the EPA. Top Tier is a voluntary standard that most major oil companies have adopted, including Shell, ExxonMobil, BP, Chevron, and Phillips. Fuel system cleaners (available at parts stores) also can be used to keep an engine clean.
An older vehicle with high mileage that develops mild knocking may benefit from a tank or two of premium (or midgrade), but if the detonation continues, the engine should be checked by a mechanic before it incurs serious damage.
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