Selecting the Right Octane Fuel

Does it Really Matter What Octane I use?

So, you purchased a fly new ride but are starting to feel the pinch at the pump paying extra for premium fuel. Do you really need to use a higher octane premium fuel? Premium gas costs 15 to 20 cents per gallon more than regular. That extra can add $200 or more a year in extra costs depending on your driving habits.

The old adage is unless your engine is knocking, buying higher octane gasoline is a waste of money, but some vehicles actually require high-octane. Whats the best method to determine what your car requires?

The recommended fuel for most vehicles is regular 87 octane fuel. But what if your owner’s manual recommends or requires premium fuel 91-94 octane? There is a subtle difference between recommended and required. Often when auto makers “recommend” premium fuel they have certified the vehicle’s EPA fuel economy with higher octane to achieve a better MPG or CO₂ emissions rating. The higher rating may not lead to cheaper cost per mile, but helps a manufacturer achieve mandated emissions or CAFE fuel economy requirements.

If premium is required for your vehicle then using a lower octane may void your warranty.

• Step 1. Read Your Owners Manual.
• Step 2. Understand that in several cases auto manufacturers “suggest” or “recommend” but do not “require” high-octane .
• Step 3. Review these”Required” and “Recommended” Premium Fuel Lists to see what your car requires.
• Step 4. If your engine knocks or pings during combustion at a lower octane, switch to a higher grade fuel.

What is octane rating?

In the U.S., unleaded gasoline typically has octane ratings of 87 (regular), 88–90 (midgrade), and 91–94 (premium). Octane rating is the measure of a fuel’s ability to resist “knocking” or “pinging” during combustion, caused by the air/fuel mixture detonating prematurely in the engine.

 Why do some manufacturers require or recommend the use of higher octane gasoline?

Higher octane fuels are often required or recommended for engines that use a higher compression ratio and/or use superchargers or turbochargers to force more air into the engine. Increasing pressure in the cylinder allows an engine to extract more mechanical energy from a given air/fuel mixture but requires higher octane fuel to keep the mixture from pre-detonating. In these engines, high-octane fuel will improve performance and fuel economy.

Will using a higher octane fuel than required improve fuel economy or performance?

It depends. For most vehicles, higher octane fuel may improve performance and gas mileage and reduce carbon dioxide (CO₂) emissions by a few percent during severe duty operation, such as towing a trailer or carrying heavy loads, especially in hot weather. However, under normal driving conditions, you may get little to no benefit.

What if I use a lower octane fuel than required for my vehicle?

Using a lower octane fuel than required can cause the engine to run poorly and can damage the engine and emissions control system over time. It may also void your warranty. In older vehicles, the engine can make an audible “knocking” or “pinging” sound. Many newer vehicles can adjust the spark timing to reduce knock, but engine power and fuel economy will still suffer.

 Is higher octane fuel worth the extra cost?

If your vehicle requires midgrade or premium fuel, absolutely. If your owner’s manual says your vehicle doesn’t require premium but says that your vehicle will run better on higher octane fuel, it’s really up to you. The cost increase is typically higher than the fuel savings. However, lowering CO₂ emissions and decreasing petroleum usage by even a small amount may be more important than cost to some consumers.

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Image Credit: Demond Henderson

Source: fueleconomy.gov and Edmunds.com