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Do you have to use premium gasoline in your vehicle, or does your vehicle's manufacturer only recommend it? The answer could save you roughly $200 a year at the pump.

First, you need to find out what your vehicle’s manufacturer recommends. To figure that out, take a look at the owner’s manual, where it will be clearly spelled out. Also, there is a sticker inside the fuel door that indicates the fuel requirements for your car.  Vehicles that require premium fuel will have one that says “Premium Unleaded Fuel Only,” with a number that indicates the minimum octane rating. Note that many vehicles have a premium fuel recommendation,but that doesn’t mean that premium fuel is requiredin order to operate without damage to the engine.

Using the proper octane fuel in your vehicle will help it achieve maximum engine performance, giving the driver access to the most horsepower and torque the engine can offer. Fuel economy may be reduced if you put in a lower-grade octane than is recommended, though experts say the difference is usually negligible and can be overcome by being more conscience of your driving style.

The Difference Between Premium and Regular Gas

Simply stated, premium gas has a higher octane level than regular gasoline. The octane rating of gasoline determines how likely it is for engine combustion to occur at the wrong time. The higher the octane level, the less likely the combustion will occur at any time other than when it was designed to occur.

This mistimed explosion is known as “pre-ignition,” or an engine knock, simply because the sound resembles a knock or ping. Gasoline with a higher octane rating is designed to resist engine knock. Your vehicle may also emit lower-level pings when mistimed combustion occurs. An occasional ping or a knock is most likely not harmful to your vehicle, but frequent knocking can hasten the demise of your engine.

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Modern vehicles are designed to include knock sensors, which can change the timing of a spark plug to help prevent engine knock. Cars with a premium fuel recommendation can run normally on lower-octane fuel, but you won’t realize the car’s full potential without higher-octane fuel. 

What if your engine knocks no matter what the grade of fuel you put into it? When you have consistent engine knock, you should bring it to a mechanic immediately, as the situation could lead to catastrophic and expensive-to-repair engine failure. Any consistent rattling or noise coming from your engine means that it’s time for a trip to the repair shop.

87, 89, 91, and 93 Octane Gasoline

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Laws regulating which octane levels can be listed as premium, midgrade, or regular vary from state-to-state. Premium gas is usually considered to be any gasoline that has an octane level of 91 or higher. You’ll usually see these listed on pumps as 91 or 93. Sometimes, 93 octane will be listed as “super-premium” or “ultra.” Unleaded gasoline is usually considered to be “regular” when it is 87 octane. Some gas stations will list 89 octane as “midgrade.” A fuel’s octane will be listed on the gas pump, and regular-grade gas is usually the cheapest, while premium gas is the most expensive.

If your vehicle’s manual simply recommends premium gasoline instead of requiring it, it may behoove you to test and see if your gasoline choice affects your vehicle’s performance enough that it’s worth spending the extra money. To do this, get your vehicle’s gas tank as close to empty as you dare (just under one quarter of a tank will do), fill your vehicle up with premium gasoline, and keep track of your gas mileage and any performance notes while driving through at least two full tanks of premium fuel. Then, do the same for regular fuel or midgrade, or both. If you don’t see a change when using regular or midgrade fuel, you are probably safe to save the money and continue using regular fuel.

Higher Octane Doesn’t Mean Better Performance

Higher octane doesn’t always give better performance. Performance depends on the engine’s technology, in addition to a number of other under-the-hood factors.

Using a higher octane gasoline will not help clean your engine. The U.S. Environmental Protection Agency requires all commercially sold gasoline to contain engine cleaning detergent additives that can help extend the life of your vehicle. This means that your engine will be cleaned the same by 87 octane fuel as it will by 93 octane fuel, so don't feel that it’s necessary to treat your car to a higher grade.

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Your vehicle’s warranty may stipulate which gasoline you must use. Damage to your vehicle caused by using the wrong type of fuel may not be covered. If your vehicle is leased, you’ll want to pay especially close attention to what octane you are required to fill your tank with so you do not incur additional costs at the end of your lease.

Remember, diesel fuel is not an acceptable substitute for any grade of gasoline and can cause significant harm to your engine. Most diesel pump nozzles are designed to be larger than a gasoline nozzle and will not easily fit into a gas tank for filling. At many stations, the gasoline and diesel pumps are also different colors.