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What Happens if You Mix Premium and Regular Gas?

What Happens if You Mix Premium and Regular Gas?

Have you ever accidentally put the wrong gas grade in your car and wondered what will happen when mixing premium and regular gas?

Mixing premium and regular gas is not generally recommended, but doing so will have minimal impact on a vehicle’s immediate performance. Only premium cars that require higher octane gasoline may see a minor performance decrease or engine knocking.

With that in mind, that high-level answer does come with a few caveats!

So in this article, I’ll dig deeper into premium and regular gas, and the effects mixing them could have on your car. 

Mixing Premium Gas with Regular Gas

It’s not once or twice that I’ve found myself stuck with no gas for my premium car. But I can assure you that on those few occasions, my vehicle survived with the regular gas!

If you mix premium gas (higher octane) and regular fuel (lower octane), the result is a fuel tank with an octane rating of a mix between the two gas types (mid-grade).

Looking at it from a numerical standpoint, if you were to mix equal parts of a regular gas (grade 87) with premium gas (grade 91), you’d end up with an effective combined grade of 89!

Of course, this will depend on what quantity of each you have added!

A lower octane for premium cars will result in reduced performance. 

Having said that, if your car requires regular fuel, the best thing to do is fill up with regular fuel. Using premium fuel will have no added benefits.

And if you’re using a premium car, refuel it with the good stuff (if you can)!

Otherwise, if there are no premium pumps and you fear risking your car knocking, don’t worry. Fill up with just enough regular gas to reach the next nearest station.

Today, octane boosters are also available at many pump stations.

These are highly beneficial if you don’t want to take any chances with your car engine. You can purchase one and boost the octane level in your fuel tank.

What Happens When You Mix Premium with Regular Gas in a Regular Gas Vehicle?

Using premium gas in a regular gas car has no benefit in most cars.

Here’s what you need to know about what to expect when you add premium gas to a regular car!

1. There May Be No Extra Benefits if the Car Doesn’t Need Premium Gas

According to the Federal Trade Commission, using gasoline with a higher octane rating than the recommended one often brings zero benefits.

Your engine will not perform faster or any better than before. It only costs you more.

That being said, on some occasions, mixing premium gas and regular gas may result in a blend that causes your car to run a little faster or get a mileage that’s a bit better.

2. Premium Gas and Regular Gas Have Varying Octane Ratings

While some states classify gasoline as premium when the octane rating is 92, some do so with only 90.

Most gas stations stock three grades of octane: 

  • Regular grade: 87 octanes
  • Mid-grade: 89 octanes
  • Premium grade: 91-93 octanes

Therefore, you may find the premium gas you’ve refilled your car with isn’t truly a high-octane fuel.

3. Heavier Cars or Turbochargers Need Premium Gas

Have you got a regular car? Is it a heavy-engine car or one with turbochargers?

If you have a regular car, then there’s no need to use premium gas. You’ll only be spending more for virtually no benefit.

However, if you own a car with turbochargers or a heavy engine, you need to use high-octane gas. That is because these kinds of vehicles come with higher compression ratios, and failure to use premium fuel may result in knocking.

What’s more, if you own an older car, I recommend using premium gas instead of regular.

What Happens if You Mix Regular with Premium Gas in a Premium Gas Car?

Several years back, using regular gas with an octane rating of 87 in a premium fuel car resulted in an engine knock. This meant the car would start knocking immediately after refueling, before departing from the pump station.

But today, things are different. If you fill up your premium car with regular fuel by mistake, your car’s ECU (Engine Control Unit) will automatically adjust its engine performance and timing.

Therefore, your car will work just fine with the lower-octane gas!

However, while you can work with lower-octane fuel, it’s not advisable to do so repeatedly just because it’s a cheaper option.

The car was built to use higher-octane fuel, so the safest option is to stick with this as much as possible. 

How Does Premium Differ from Regular Gas?

To understand how premium gas differs from regular gas, you need to understand the octane rating!

Premium has a higher-octane rating than regular gas. It ranges from 91 to 93, depending on where you live.

In fact, there are some places where octane levels in premium exceed a rating of 93. On the other hand, regular gas has an octane level of 87.

The octane rating of gasoline indicates when mistimed combustion is likely to occur. A higher-octane rating means that the chances of combustion occurring at the wrong time (mistimed combustion) are slim.

Mistimed or poorly timed combustion or pre-ignition causes a ping or knocking sound. It’s the reason it is also known as ‘engine knock’.

Gasoline with higher octane rating is ideal for preventing engine knock, which perhaps would explain why sometime back people tended to use premium in regular gas vehicles.

Occasional lower-level pings are typically harmless to your vehicle. However, repetitive engine knocking accelerates wear and tear, causing damage to your engine.

Final thoughts on mixing premium and regular gas

Mixing premium and regular gas in any car is generally not advisable. If your car is a premium, use premium fuel, and if it’s a regular, use regular gas.

Mixing the two adds no benefits to a car that is supposed to use regular gas, and for a vehicle that should run on premium, it may not run as smoothly. Unless under unavoidable circumstances, stick to the octane level of your car.

Before you can use premium fuel in your regular car, consult automobile experts first. However, let the common myth that premium fuel on regular cars lead to better handling and car performance not misguide you. 

What is essential for any vehicle is proper maintenance and regular checkups. With the two, your car’s performance will always be top-notch.

Frequently Asked Questions (FAQs)

Below are some frequently asked questions about mixing premium and regular gas.

Can You Mix Regular and Premium Gas at the Pump?

You can mix regular and premium gas to get a mid-grade octane. In fact, this is what most pump stations do to get a mid-grade-level octane gas.

However, mixing premium and regular in a premium car will reduce efficiency and cause it to lose its power. With every drop of lower octane, chances are it will affect your car’s performance over time.

You see, if your car is a regular gas vehicle, it will run well on pure low-octane gas. Mixing the regular gas with premium is a waste of money as it adds no benefits.

How Do I Know the Type of Gas to Use?

When buying a car, you must establish the type of gas it runs on. 

To do so, take a look at the inner side of the fuel door. You will find a label indicating the kind of fuel you should use on that car. 

Do Turbocharged Cars Need Premium Fuel?

Generally, most manufacturers of cars with turbochargers recommend using premium fuel on them. 

But to be sure, always check your owner’s manual. It specifies every detail about your vehicle, including the gas type you should use.

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Zach Reed

Hi, I'm the founder of! Having owned a wide variety of vehicles in my life, I was astounded at how hard it can be to find answers to common automotive questions. Rather than sit idly, I decided to create this website to help others!