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The Daily Cardinal Est. 1892
Friday, May 17, 2024

Ask Mr. Scientist: Gas Issues

Dear Mr. Scientist,

Can lower octane gas be used in premium gas vehicles?

—Dawn M.

It depends. First, a little background information is in order. Most automobile engines work on a four-stroke cycle known as the Otto cycle. The cycle consists of one stroke to bring in fuel and air, another to compress the gases, a third to ignite the mixture and a fourth stroke to clear the spent gases out. Sometimes the fuel mixture can ignite prematurely during the compression stroke which is known as “preignition” or “knocking.”

Some cars have engines where the volume of the fuel cylinder when the piston is at its lowest point is a lot larger than the volume with the piston at its highest point. In these types of engines preignition is more likely to occur so manufacturers suggest using only premium gasoline which contains a high level of octane. Octane is a hydrocarbon that can be compressed a lot without igniting, so there is little risk of any preignition occurring, but these fuels are also more expensive.

Nowadays, most engines have a knock sensor which adjusts the timing of the engine if low-octane fuel is used to avoid preignition. The bottom line is that it is up to you. If the owner’s manual doesn’t make any mention of using only premium gasoline, then lower octane gas should be OK.

Ask Mr. Scientist is written by Michael Leitch. If you have a burning science question you want him to answer, tweet @DC_Science or email it to

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