What Happens If You Mix Premium And Regular Gas?

Can you gas grades such as 87 gas, 91 gas, or 93 gas? What about premium gas and regular gas? Here's everything you need to know about mixing gas grades.

While most gas-powered cars run on Regular fuel, some require Premium. Besides the heftier price tag, the main difference is the octane rating, or grade. Regular gas generally has a grade 87, while Premium ranges between 91 and 94.

The higher the octane rating, the more resistant the fuel is to early detonation.

Can you mix Premium and Regular gas? Combining fuel grades basically just alters the octane rating of what’s in the tank. In fact, many gas stations offer an 89-octane “Midgrade” option that’s merely a blend of Regular and Premium.

So, is it bad to mix gas grades?

In cars built for Regular, adding in some higher-octane fuel shouldn’t cause any harm.

However, putting Regular fuel in a Premium car will not only lead to reduced performance but may result in lasting engine damage.

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What Happens If You Put Regular Gas In A Premium Car?

Filling Gas In A Premium Car

Higher-compression engines, like those with forced induction (i.e., turbocharged), are designed to squeeze as much performance out of a motor as possible.

However, they also generate more pressure and heat, which may cause lower-octane fuel to ignite early, an issue that can lead to engine knock.

Engine knock, or “pinging,” essentially means the air/fuel mixture inside the combustion chamber is not igniting evenly. While the occasional knock is fine, persistent knocking can cause lasting damage to vital engine components, including the pistons, crankshaft bearings, and cylinder walls.

Not sure what engine knock sounds like? This short video from YouTube’s Motorcarnut gives a great example.

Due to Premium fuel’s higher-octane rating, it’s less likely to ignite early. This gives the vehicle’s Electronic Control Unit (ECU) time to optimize detonation and, thus, performance and efficiency.

Engine knock can stem from several things, like bad spark plugs or carbon buildup, but low-octane fuel is one of the most common.

What Happens If You Put Premium Gas In A Regular Car?

Crop man refueling car on filling station

The benefit of Premium fuel is that it allows the ECU time to optimize detonation. However, a car built for Regular fuel doesn’t generate enough pressure or heat for early ignition to be an issue.

While filling up with Premium might sound like a way to pamper your car, there’s really no benefit if it’s made for a lower-octane rating.

Can you mix 87 and 91 gas? Sure, but you’re essentially just throwing away money. Instead, save yourself roughly 50-cents per gallon and opt for the gas grade your car is built for.

How Do You Know If Your Car Takes Regular Or Premium Fuel?

Fuel Rating Label Octane Number

You’ll find the required fuel grade on a label inside the gas door. With time, though, this label may fade or fall off. Thankfully, the owner’s manual will also detail the octane rating your engine is designed for.

Finally, you can also provide your car’s VIN to a local dealer to find out the correct gas grade.

So, Can You Mix Different Grades Of Gas?

Crop hands crossing fuel nozzles

There are a lot of things you can do to extend the life of your vehicle. However, filling the gas tank with the wrong fuel grade is not one of them.

If you accidentally add Premium fuel to a car built for Regular, nothing bad will happen to the engine, and you can drive without worry. However, you also won’t get any benefits, so don’t expect improved fuel economy or more power.

Mistakenly adding Regular to a car made for Premium isn’t a crisis either, so long as it doesn’t happen often.

If you do notice the engine knocking after adding Regular fuel, you may be able to resolve the issue by pouring an octane booster into the tank.

Besides using the correct fuel grade, only filling up at Top-Tier gas stations is another way to extend your vehicle’s longevity.

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Joshua Barrett

Josh Barrett is a writer hailing from the great state of Alaska. While describing himself in the third person is not his forte, writing about any and all things automotive – is. After 13+ years hustling in the exciting world of car sales, he took off to travel the world with his dog Teemo.

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