With the price of gas these days, it’s tempting to select the cheapest option at the gas pump. But will saving a few bucks filling up your tank with less expensive “regular” gas end up hurting your car’s engine?
Well, the answer to that question hinges on the car you drive, how you drive and the conditions you drive in. Here’s everything you need to know.
Premium Fuel “Required”
Check your car’s owner’s manual. If it says premium fuel is required, the safest thing to do is to stick with premium. Especially if you’ve acquired an older model. We wouldn’t dream of putting 87 octane in an older, less sophisticated car that requires premium like, say, a 2001 BMW M3 or a 1969 Camaro ZL1.
But doing so in a turbocharged 2023 M3 or a supercharged 2023 Camaro ZL1 poses a far, far lower risk of damage, even though the later-model engines are much more powerful. Yes, you’ll lose some power at full whack, and your fuel economy may drop a bit, but you won’t hurt anything if the car is driven mildly in normal conditions. The engine’s computer controls will compensate for the lower octane fuel and protect the engine from knock.
And if you’re worried that using regular instead of premium fuel will “gum” up the inside of your engine, don’t be. That’s a myth. Gasoline’s octane level has nothing to do with the contamination of internal engine parts.
Premium Fuel “Recommended”
When automakers recommend (rather than require) premium, it’s all about them: they want to boast the biggest power and torque numbers possible on the spec sheet. That is, the engine will produce the advertised peak power and/or torque on premium, but no harm will come if you choose to run on lower octane.
In this case, you have the manufacturer’s blessing to try 87 octane to your heart’s content. There’s no risk at all. Again, the electronic engine controls will adapt to the lower octane, preventing knock at the cost of a bit of power.
However, if your situation involves some combination of towing, using the throttle aggressively and driving in hot conditions, like a summer day in Phoenix, Arizona, spring for the higher-octane premium, especially if you have a turbocharged engine.
Knock, Knock, Who’s There? Octane
The difference between “regular”, mid-grade and premium gasoline is the octane rating. Octane is a gasoline additive that is needed for the proper functioning of modern engines. Premium gasoline has higher levels of octane than mid-grade or regular. The number on the label at the pump (85, 87, 89, 91, or 93) is the octane rating of the fuel, and the higher the octane rating the higher the price per gallon.
Octane is important, because it helps prevent engine knock, which can destroy an engine’s pistons, cylinder walls, cylinder head and more over time. Knock occurs when a portion of the unburned mixture of fuel and air inside your engine’s combustion chambers combusts in an uncontrolled fashion, independently of the controlled combustion process.
The higher a fuel’s octane level, the less likely knock is to occur. And automakers rely on octane’s knock-nullifying quality to extract maximum performance and efficiency from engines.
However, the real magic happens inside today’s sophisticated electronic engine controls that detect knock, and deploy a variety of countermeasures, such as reducing the engine’s ignition advance, to quell it and prevent it from recurring. Modern turbocharged engines can also reduce boost. Over the last 10 years or so this technology has unlocked greater flexibility when it comes to the grade of fuels engines can safely consume.
Using cheaper lower-octane fuel may sap some performance, but only at wide open throttle—
you know when you floor the gas pedal. And the losses are usually quite small. A normally aspirated engine may lose only 5-10 horsepower, while a turbocharged engine could lose about twice that.
Knock is not really associated with part-throttle operation. If you tend to accelerate moderately, you probably won’t even feel the difference.
Conduct Your Own Experiment
If your car only recommends (but does not require) premium, we suggest you conduct your own experiment. Fill up with a few tankfuls of lower-octane fuel and log your fuel economy. If you can’t feel (or don’t mind) the mild change in power output at full throttle and the observed fuel economy is largely the same, stick with the lower grade stuff. You’ll save some money and won’t risk any damage to your engine.
But take the time to do the math and see if it pencils out. In extreme cases the drop in fuel economy penalty might offset the cheaper price of the lower-octane fuel.
In a Nutshell
Overall, if you drive most modern cars conservatively, in mild weather, there’s no real benefit to using premium fuel. And the converse is also broadly true — if your car recommends 87 octane you’re wasting your money using premium.
Just remember that knock can cause catastrophic engine failure. If you hear it, your car’s engine is clearly asking for the “the good stuff”. Back off the throttle, get to the pump and give it what it wants.
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