Can you mix regular and premium gas? What to know during fuel shortage in Southeast

·4 min read

Colonial Pipeline has restarted operations following a cyberattack, but the company said it could be days before the fuel supply returns to some level of normalcy in the Southeast.

In the meantime, drivers are searching for a quick fix to fill up their tanks amid long lines at the pumps and limited options.

For some, that means putting premium gas in a Honda — or regular unleaded in a Volvo. But don’t panic. Most experts agree drivers can fill up with a lower or higher level of octane without disastrous consequences.

Here’s what you need to know.

My car runs on regular gas. What happens if I put premium in it?

According to one Honda dealer, “nothing significant will happen” if a driver puts premium gas in a car that doesn’t need it.

Some people will fill up with premium believing it will help clean out parts of their car’s fuel system, but experts say that’s a myth.

“An engine not as highly stressed that is designed to burn 87-octane gas doesn’t run much risk of detonation, so it gains no benefit from using premium,” The New York Times previously reported. “In those cars, the five or more extra dollars spent on premium for each tankful is simply wasted, the equivalent of feeding Zabar’s pumpernickel to the Central Park pigeons.”

Can I put unleaded fuel in a car that takes premium?

According to Fuel Express, you can put regular gas in your car or truck even if the manufacturer recommends premium. But if they require premium, then pumping unleaded might cause issues.

“Just because premium is recommended doesn’t mean you have to use it; you can easily use regular gas without compromising the engine,” Fuel Express said.

Others may disagree.

Citing World Toyota’s Service Center, 11Alive reported drivers should not put regular gas in a vehicle that takes premium because the lower octane levels found in unleaded gas could create “knocking” that damages the vehicle’s motor. It may also void your warranty.

Octane ratings refer to the “87” or “89” you often see on regular and plus gas pumps. The higher the octane rating, the less likely a car will experience a “mistime combustion,” which creates the engine knock sound, according to The Drive. A higher-octane gas, such as premium, helps prevent engine knock.

In older cars that require premium, The Drive reported fueling with 87 octane would almost immediately cause the engine to start knocking. But newer model cars are better equipped to handle it.

“If you mistakenly fill up with regular fuel, your car’s ECU will adjust engine timing and performance to work with the lower-octane fuel,” The Drive said. “In most cases, this is OK for the times when there are no premium pumps around, but it’s not ideal to run the cheapest fuel possible for extended periods of time.”

Can I mix premium and unleaded gas?

Yes, drivers can mix the two types of fuel. The combined gas types will result in an octane level somewhere in the middle — something the vehicle “will survive,” according to The Drive.

“That said, if your vehicle requires premium fuel, it’s a good idea to top it off with the good stuff as soon as you’re able,” the website said. “If you’re really worried about the engine developing a knock, you can add just enough regular fuel to get you to the next station, but be sure you have enough fuel to reach the destination.”

What about diesel?

Do not under any circumstance put diesel in a car that takes gas, or vice versa.

According to Fuel Express, putting unleaded gas in a diesel vehicle will remove lubrication on its parts and “cause big damage.” A car that was mistakenly filled up with diesel, meanwhile, might run for a few miles before it loses power.

“You’ll need to flush out your fuel lines and refill the car or truck with diesel, but you’ll be able to drive it again,” Fuel Express said.

If a driver mistakenly fills up with diesel or gas, Allstate said they should not turn the car on and call a mechanic instead.

“Rather than running the engine, have your car towed to a professional who can ensure the fuel system is drained and cleaned,” the insurance provider said.

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