What do the different grades of gasoline mean?

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What do the different grades of gasoline mean?

You pull up to a gas station, blasting Katy Perry and singing your heart out (or stoically listening to NPR — I don’t know your life!). You get out, pop up your gas hatch, and get ready to fill your car with sweet, sweet oil. But wait — there are three different types of gasoline at the pump! You collapse to the ground, weeping. You never drive again.

Or maybe you just quietly wonder what the different types of gasoline are and why there need to be different types of gasoline in the first place! And then you absent-mindedly Google it, and then you end up here, where I explain that gasoline grades are based on "octane ratings."

Typically, you’ll find three grades of gasoline at the pump: Regular (87), Plus (89), and Premium (92). But don’t be fooled by the names — if you put Premium grade gasoline in your Honda Civic, you’re not going to have a premium experience.

Using a higher octane fuel won’t help your regular, consumer-level car go faster or perform better. In fact, it can hurt your engine. Octane ratings tell you how long the fuel can withstand pressure without self-igniting, which is important to get right.

To put it as simply as possible: octane ratings tell you when your gasoline is going to explode. Don’t worry, it’s a good explosion — the type of explosion that propels your car forward. Car engines have pistons inside that move up and down to help squeeze the gasoline and make it hot, and if the gasoline explodes at the wrong time, it messes up the pistons. This is what causes the "knocking" sound in a car engine that isn’t using the right fuel.

If you’re driving a large truck or high-performance racing vehicle, however, you’ll need that higher octane fuel. The engines in these vehicles put a lot more pressure on the gasoline. Higher octane fuel can withstand that pressure, whereas lower octane fuel will ignite all at once and melt the engine. Typically, you don’t want to melt the engine.

But nameless internet writer, you may be thinking,_ I live on a mountain and my gasoline grades are different than those you listed above!_ You’re correct! If you live in an elevated area, such as Denver, Colorado, you may use a lower octane fuel in your car or truck. Why? The higher you get above sea level, the less oxygen there is in the air, which can affect how multiple things, including gasoline, burn.

What if you accidentally put the wrong gas in your car? Don’t worry — most modern engines have electronic sensors and controls that can actually tell what type of gasoline you’re using and change the way the engine works accordingly. That doesn’t mean you should go around playing with higher grade gasoline, however — always use the grade of gasoline recommended by your car’s owner’s manual.

Image: Kevin Mosley