a hand filling fuel in a car

What Gasoline Should I Use? | Octane Ratings & Your Car

With gasoline being as expensive as it is, many people want to know if it’s worth it to pay the extra money for mid-grade/plus, premium, or even super premium gasoline. Is it just a marketing gimmick?

What’s the Right Type of Fuel for My Vehicle?

Most gas stations offer a choice between 3 different octane levels:

  • Regular (85-88, usually 87)
  • Mid-Grade/Plus (88-90, usually 89)
  • Premium (91-93, usually 92)

Some gas stations offer additional octane grades with names like “special,” “plus,” and “super.” “Super premium” normally has an octane rating of 93.

So, which one should you use?

The answer is very simple: consult your owner’s manual! 

It’s so obvious, but many people don’t remember to check the manual before choosing the type of gasoline for the car. If it says regular (87), use regular. If it says premium (91), use premium. Contrary to common belief, octane ratings do not indicate how many miles you get per gallon or how much power the fuel delivers.

While higher prices normally indicate higher quality (“you get what you pay for”), in the case of gasoline, there is no increase in performance for engines that are designed to run on regular gas.

The different types of fuel are designed for different types of engines. The only difference separating the different gas grades is the amount of octane present in the fuel.

Recommended vs Required

Some car manufacturers “recommend” premium while others “require” premium. If it requires premium, definitely use it. Trying to save a couple of dollars at the pump is not worth the LARGE costs of engine damage and repair. Normally, only high-end, high-compression vehicles require premium gasoline.

If it only “recommends” premium, then you won’t do any damage by using regular gas, but you could get some better performance with “premium.” Consider using premium gas when you anticipate extra demand on the engine, such as driving up steep hills or pulling heavy weight.

If you wanted to save money, you can probably still fill up with regular gas most of the time. And at an extra 20-50 cents more, that’s around $200 more in your pocket every year.

What are octane ratings?

The fuel’s octane rating measures the fuel’s ability to withstand pressure and resist “knocking” or “pinging,” which can cause engine damage.

Knocking or pinging are noises that your engine makes when there is an uneven combustion in one or more of your car’s cylinders. When the piston moves up and compresses the fuel/air mixture, the spark plug is supposed to rapidly burn the fuel, which causes the piston to move down very fast.

Sometimes, however, there is a “pre-ignition” during the compression process which creates a small explosion. This normally happens when you have a high-compression engine with a low-octane fuel. This is bad and can cause the fire from the compression to collide with the fire from the spark plug. As a result, you may hear a “ping” if the fire is small enough, or a “knock” if it is big enough.

The image below shows the two “explosions” colliding to create a “pre-ignition” knock/ping:

This is why it’s important to check the owner’s manual/handbook. The recommended octane level will completely depend on the design of the engine. Higher octane fuel burns slower, reducing the chance of pinging or knocking in high-compression engines.

Don’t be too worried about small pings and light knocks. However, if you experience loud or heavy knocking using fuel with the recommended octane rating, see your authorized dealer to prevent any further damage to your engine.

Still, most cars are designed to run on regular gas. Anyone who says that premium gas will give you more mileage or power is living in a fantasy land. High-octane gas is basically a protection for high compression engines.

What is a knock-sensor?

Most cars nowadays (1997 or later) contain a knock-sensor that detects the compression detonation and delays the spark to minimize knocking/pinging. While this is good for protecting your engine from “pre-ignition” knocking, in higher performance vehicles, the spark delay gives you less power and worse mileage.

Again, it’s simple: use the octane level specified by your owner’s manual.

Does premium gas help cleanse my engine?

You may hear the claim that premium and high-octane gas contains more detergents and therefore can help clean your engine. While premium gas may contain more detergents, regular gasoline has more than enough detergents to keep your engine clean.

If you have a noticeably dirty engine, then use one of the many great engine additives on the market.

Is there a difference between gas from different brands?

While there are no really good studies that validate quality claims of different brands of gasoline, there is indeed a difference. In fact, if you are looking to improve your MPG, you’ll find much more success trying a different brand rather than a higher octane level.

The main difference between different brands of gasoline are the contents of the additives. In 2004, some large car manufacturers were unhappy with the amount of deposits in their engines so they got together to create new gasoline standards. These standards are stricter than the federal Environmental Protection Agency standards and are given the name “Top Tier” gas.

They contain an enhanced additive package that includes antioxidants, oxygenates, and corrosion inhibitors.

Some gas stations only sell “Top Tier” gas: 76, Chevron, CITGO, Costco Gasoline, Exxon, Mobil, QT, Shamrock, Shell, Sinclair, Texaco, and Valero.

Here’s the full list of Top Tier Detergent Gasoline Licensed Brands.

If you drive a high-end car and don’t want any deposits to build up, you should probably use Top Tier fuel most of the time. Still, you can usually get rid of any carbon deposits with a few bottles of engine cleaner.

In conclusion, unless you want to increase the portfolios of the super-rich, check your owner’s manual for the recommended gasoline octane level and don’t spend any extra money on higher octane fuels.

If you have any questions, don’t hesitate to contact Auto Simple.

Learn more car maintenance tips.

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