Automotive Tips

What Do Octane Numbers Mean?

gasfillingWhen you pull into the gas station, you’ve undoubtedly noticed several types of fuel to choose from, but how do you know which one is right for your vehicle? Sure premium gas is more expensive than regular, but what’s the real difference? The double-digit numbers ranging from 87 to 92 are often called the “octane rating” or “octane number”. They distinguish the various fuel types, but these numbers hardly give a clue as to what sets them apart. To understand octane ratings, you’ll need an overview of how your engine converts gasoline into power.

In an internal combustion engine, fuel and air are compressed inside the cylinder and ignited with a spark from the spark plug. If the compressed fuel/air mixture ignites spontaneously before the spark plug can do its job, a rattling or pinging sound known as “engine knock” may occur. While infrequent light knocking won’t harm your vehicle’s engine, a persistent or heavy knock can cause engine damage if left unchecked.

Using the correct grade of gasoline in your vehicle prevents engine knocking—each grade has an octane rating signifying how much compression the fuel can withstand before igniting on its own. These number ratings measure resistance to engine knock. A higher octane rating indicates the ability of gasoline to handle higher engine compression ratios without igniting prematurely and causing engine knock.

Look for the bright yellow stickers located on each gas pump to choose the correct octane grade for your vehicle. Most gas stations offer a choice of three octane grades:

  • Regular—Usually 87 octane, and it ignites with the least amount of compression.
  • Mid-grade—89 octane fuel can handle more compression than regular octane fuel.
  • Premium—92 or 93 higher-octane fuel is used in high compression engines due to its ability to resist engine knock.

Jiffy Lube of Southern California recommends checking your vehicle owner’s manual to be certain of the correct octane level. Regular octane is recommended for most vehicles except for those with high performance engines. The only reason to switch to a higher octane gasoline is if you notice knocking in your engine when using the recommended grade of fuel. If this happens, you can try filling up with the next highest octane grade.

While you might occasionally neglect to answer a knock at your home’s front door, it’s best not to ignore a knock in your vehicle’s engine. To keep your ride smooth, dependable, and quiet, use the recommended octane grade of fuel for your vehicle and remember to obtain regular engine services from your neighborhood Jiffy Lube.

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