Octane Rating FAQs

You've just purchased a brand new vehicle and you remember the salesperson saying you need premium fuel for it. Was he serious or was he just trying to make the vehicle feel more premium? What's the deal? Well, every owner's manual has a page dedicated to fuel recommendations and requirements. Your manual will recommend a certain grade and will also tell you the minimum grade you can use, if applicable. That's the gist. Here are the details:

What do those numbers actually mean?

The octane rating or AKI (anti-knock index) of a fuel indicates the ratio of isooctane to heptane in the fuel. Premium gasoline, having a rating of 91 or higher, is required for some vehicles and recommended for others. Most vehicles can run on regular, low grade gas such as 87 AKI. 89 AKI is called mid-grade gas. A car that requires premium fuel has what is call a high-compression engine.

Can I use a higher AKI/Octane rating than recommended?

You can, but the benefits this used to have don't apply today. Premium fuels used to contain more detergents than regular fuels, which would help protect your engine. Today, it's just all about the octane ratio and your engine type.

Can I use a lower rating than recommended?

It depends on the wording in your user's manual. If premium fuel is required, you should not use fuel with a lower AKI than is required. If a certain AKI is recommended, you can use a lower grade. Just check the manual for information. It might say 89 is the minimum grade you should use, for example. In some cases, using the minimum grade can cause some knocking noises but will not damage the engine. Your manual should give you this information. Using a lower grade than recommended will probably reduce the performance of your vehicle, but only while that fuel is being used. Using a lower grade than the required grade can cause engine damage.

What about the E numbers?

E10 means the fuel is 10% ethanol. E15 means it's 15% ethanol, and so on. Most gas stations don't sell fuel that is more than 10% ethanol, and most vehicles can handle up to 10% ethanol. Therefore, ethanol usually isn't a concern. Watch out for the rare case in which you find a higher ethanol rating, though. Read your manual to find out if your vehicle can use it.

Does premium fuel give me better efficiency?

Not really. You won't save significant money or gain much efficiency by purchasing a higher grade of fuel; in most cases, at least.

What can happen if I don't follow the recommendations or requirements?

Your engine's pistons will be under greater pressure and your vehicle's performance will temporarily decrease. Having a heavy foot and ignoring fuel grade requirements will eventually lead to damage and breakdowns. Going against recommendations could have the same effect somewhere down the line, but it's not likely in the short term. We suggest you stay in bounds with regard to your user's manual.

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