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Which Grade of Gasoline Should I Use?

Young woman refueling car at self service gas station

When you pull up to the pump and select which type of gas to buy, how do you know which kind to use? You want your car to last as long as possible but want to save as much money as you can, too. Here’s the breakdown of the different grades of gas and what they mean for your car.

What Is An Octane Rating?

If you’ve ever pumped gas, you’ve seen the big yellow square on the pumps with large numbers on them. That yellow sticker is an octane label showing that pump’s minimum octane rating — but what does that mean?

Scientifically speaking, octane is a hydrocarbon derived from processing petroleum. However, in terms of fuel for your car, an octane rating measures a fuel’s ability to resist “knocking” or “pinging” during combustion, caused by the air/fuel mixture detonating prematurely in the engine.

The “(R+M)/2 Method” on the label refers to the octane testing method used, where R is Research Octane Number and M is Motor Octane Number.

Retail gasoline stations in the United States sell three main grades of gasoline based on the octane level:

  • Regular (the lowest octane fuel – generally 87)
  • Midgrade (the middle range octane fuel – generally 89-90)
  • Premium (the highest octane fuel – generally 91-94)

Some stations have different names for these grades of gasoline, such as unleaded, super, or super-premium, but they all refer to the octane rating.

Which Grade Should I Use?

You should be using the octane rating required for your vehicle by the manufacturer. You can check your owner’s manual to find out which grade is required. Most vehicles that run on gasoline (as opposed to diesel) are designed to run on 87 octane (regular or unleaded), but others use higher octane fuel (like midgrade or premium).

How Does Each Grade Affect My Car?

Using a grade of gasoline that is too low for your car can damage the engine and emissions control system over time and your fuel economy will suffer.

Repetitive tapping or a pinging sound from your engine that becomes louder and faster as you accelerate is a classic sign of engine knock. This usually happens in older vehicles, while many newer vehicles can adjust the spark timing to reduce knock. Either way, knocking is an indication that the engine may be running poorly due to running on the wrong grade of gasoline.

Using a higher octane fuel than your car requires may improve performance and gas mileage on some cars. It could also reduce carbon dioxide (CO2) emissions by a few percentage points during heavy-duty operation (e.g., towing a trailer or carrying heavy loads), especially in hot weather. However, under average driving conditions, you are likely to get little to no benefit. Therefore, it’s rarely worth the extra cost at the pump.

What About Other Types?

You may see even more options at certain gas stations when looking at the pump. One of those is usually the addition of ethanol. It has a much higher octane rating (about 109) than gasoline and is usually blended with gasoline to help boost its octane rating. In fact, most gasoline in the U.S. contains up to 10% ethanol, but some stations offer blends of up to 15%. Most vehicle manufacturers approve this blend in recent-model vehicles, but it’s up to you to decide if you want to spend the extra few cents per gallon or not.

In areas with high elevation, gasoline with an octane rating of 85 may be available. In these areas, the barometric pressure is lower, so most older carbureted engines tolerate it fairly well, and it is cheaper. Generally, it is not advised to use this grade for newer vehicles and even older ones.

Whether you use regular or premium-grade gas, you can be sure you’re getting the best grade on car insurance with a free quote from Freeway Insurance. Freeway Insurance can help you shop for the best auto insurance you can get at a price you can afford. Call (800) 777-5620 today to speak to a live agent.

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