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Which gas should you use in your car?

Stick to the manufacturer's requirements at least, but can you level up to premium or bio-fuel?

While most cars run on regular gas, some models specify a different octane level to make the engine run smoothly. You can use a higher octane in a car requiring only regular gas, but beware of using the wrong octane for a luxury or performance car. In addition, some vehicles can run on diesel or bio-fuels, and you’ll want to follow the manufacturer’s recommendations when fueling up these rides.

Which type of gas should I use in my car?

You can probably choose regular gas at the pump since most cars in the US run on 87-octane gas.

However, the best place to look for your car’s recommended type of gas is the owner’s manual, though you might find labels in several places.

  • Fuel door. You might see a sign like “Diesel only” directing you to a certain type of fuel.
  • Gas cap. Flex-fuel vehicles may have an orange gas cap to mark its bio-fuel capabilities.
  • Fuel gauge or fuel door lever. Diesel or flex-fuel vehicles might draw your attention to their fuel types with a label in common areas you might look just before fueling up.
  • Owner’s manual. When in doubt, your owner’s manual will show you the best type of gas or fuel to use.

Look at the sticker on the inside of your filler cap. Or check your manual for the minimum octane rating you can use in your car.

What if my car needs RON 95 or 98?

You might see these octane numbers if you’re driving a European car. However, octane ratings work differently in Europe than in the US. If you see RON 95, you can use 87-octane regular gas in your car. You’ll need 93-octane premium fuel for RON 98, although the ratings don’t transfer exactly.

What types of gas are available?

You’ll find several types of fuel sold at gas stations around the nation with important differences. Those types include:

Unleaded Regular

Regular gas typically includes an 87-octane rating. It’s the standard fuel type that most cars run on, unless you own a sports or luxury car. It’s also more flammable than other types of gas, so it tends to preignite more often than premium fuel. Regular gas works best for engines built for lower performance.

Examples of cars that use regular gas:

  • Honda Odyssey
  • Lexus ES350
  • Nissan Altima
  • Toyota Camry
  • Toyota Prius

Plus or midgrade

Plus or midgrade gas tends to include an 89-octane rating, resisting preignition more than regular fuel. However, not many cars require midgrade gas, so this option comes down to your preference. Drivers may go for midgrade gas to help with engine knocking or when their car can take regular gas but premium is recommended.

Cars that allow both regular and premium gas:

  • BMW X3
  • Chevrolet Camaro
  • Jeep Grand Cherokee
  • Lincoln MKZ
  • Nissan Sentra

Premium

Premium gas typically includes a 91- or 93-octane rating. While a variety of cars require premium fuel, many of those fall in the performance or luxury car classes. It’s also the most expensive type of gas, sometimes costing 20 cents more per gallon.

Cars that require premium gas:

  • Alfa Romeo Giulia
  • Infiniti Q70
  • Jaguar F-Pace
  • Land Rover Discovery
  • Nissan 370Z
  • Porsche Cayenne

Ethanol

Nearly all gas sold in the United States contains about 10% ethanol, a blend known as E10. Ethanol is a renewable type of fuel with a high-octane rating. This type of fuel may burn cleaner than standard gasoline, reducing emissions. However, using ethanol can lower your car’s fuel economy.

All gas-powered vehicles can use E10 gas. However, a few cars called flex-fuel vehicles can use a blend with up to 85% ethanol, called E85. E85 gas is cheaper than regular or premium gas. But you should only use fuel with a higher amount of ethanol if your car’s manufacturer specifically approves it.

Cars that use E85:

  • Buick Lucerne
  • Chevrolet Monte Carlo
  • Chevrolet Impala
  • Pontiac G6

Diesel

Diesel is a type of fuel used specifically in diesel engines. Rather than igniting the engine through a spark as with standard gasoline cars, diesel engines ignite by compressing air in the cylinder. Vehicles that run on diesel tend to get better fuel economy. Diesel fuel can also be called diesel oil.

Vehicles that can run on diesel include:

  • Mazda CX-5
  • Mercedes-Benz E350 BlueTEC
  • Land Rover Discovery
  • GMC Terrain
  • Jaguar F-Pace
  • Jeep Grand Cherokee

How do octane ratings work?

The octane rating is the number listed at the gas station’s pump, typically under the standard name for the fuel like regular, plus or premium. The most common octane ratings in the US are:

  • 87-octane for regular
  • 89-octane for plus or midgrade
  • 91- to 93-octane for premium

Some people believe the higher the octane number, the more powerful or energy-dense the fuel. But the number actually indicates how resistant that gas is to preignition, a situation that happens when the fuel ignites sooner than needed. In simple terms, the octane rating is the engine’s ability to control timing for the fuel’s ignition.

Warning! It’s important that you use the correct type of gas for your car’s engine, especially avoiding diesel or bio-fuel for gas-powered cars.

It depends on whether that octane rating is higher or lower than the recommended gas for your car.

For example, you can use a higher-octane gas like 91-octane premium if your manufacturer recommends regular 87-octane fuel. Many owner’s manuals state that your car needs at least 87-octane gas. However, you may or may not experience better efficiency by using premium gas.

What to do if I use the wrong type of gas

The safest action is to consult a mechanic. You’ll likely need to either run the car to burn off the fuel, siphon the gas tank or let a mechanic fully clean the fuel system.

This may depend on how much of the fuel you put in your car and how much you drove it afterward.

What happens to my car if I use lower-octane gas?

If your owner’s manual requires 91- or 93-octane gas, you should buy premium. In this case, your car may compress the air in the fuel tank more, leading to a higher chance of the gas igniting before it’s designed to.

Many cars that recommend premium gas can still run on regular, but it could lead to lower performance and gas mileage. Cars that require premium should not run on 87-octane gas regularly, if at all.

What is engine knocking?

When fuel and air combust within the engine before it’s designed to, the engine may make a knocking sound. This technical term for engine knock is preignition. Engine knock can cause damage to your car’s internal parts like the cylinders and pistons. Damage can eventually result in poor engine performance and lower fuel economy.

If you can’t resolve the knocking by using the manufacturer’s recommended fuel, consider going to a mechanic. This problem can worsen and lead to lower power, engine strain or even overheating.

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Bottom line

Your car may need a specific type of gas to help the engine run smoothly and prevent engine knocking, especially if it needs premium gas. Although you might pay more for gas than you’d prefer, you can save money on monthly costs when you look for the best-valued car insurance available.

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