What Happens if You Mix Premium and Regular Gas?

Those three numbers displayed on the front of a fuel pump can be confusing. Different areas or gas stations can even have different numbers, but they usually fall between 87-94. Usually, these numbers are accompanied by labels along the lines of “Regular”, “Mid-Grade, and “Premium”. 

While it’s important to understand that fuel grade is important for the health of many vehicles, it can be easy enough to mix up the numbers in your head or mistakenly hit the wrong fuel grade. This can leave many feeling confused about if their vehicle is safe to continue to drive or not. In this article, we’ll dive into what fuel grade is and what to do if you accidentally mix.

What is Fuel Grade (Octane)?

With names like Premium and Regular, many assume that the higher tiers are simply “better gas” for your vehicle. 

Instead, this number and grade system actually refers to the octane level of the fuel. Octane is the gasoline’s resistance to pre-ignition, which is when the fuel is ignited in the cylinder prior to the optimal moment. Higher octane levels will be less likely to ignite early, also commonly called “knocking”. Knocking isn’t immediately going to cause any major problems if you hear it once or twice, but a heavy and consistent knocking or pinging sound may mean your engine could end up damaged. 

So, does that mean higher octane fuel is better for your vehicle? It depends, but generally no. Vehicles with higher performance and higher compression engines are more likely to encounter pre-ignition, which means that higher-octane fuel is better for protecting them. However, the majority of economy and commuter vehicles can run the lowest grade of fuel perfectly fine. 

Fuel pump showing octane levels

What Fuel Grade Should I Use?

First and foremost, the best resource for which fuel grade is best for your vehicle is the vehicle itself. The inside of the gas cap and the owner’s manual are both common places for the manufacturer’s octane recommendation.

It’s also important to note that running higher-grade fuel in a vehicle that doesn’t need the extra protection will not result in a noticeably better driving experience, only increased spending. The benefits of running high-grade fuel are only significant in vehicles that actually need it. 

What Happens if I Mix Octane Levels?

Luckily, even if you do mix octane levels, your car will be okay. Mixing two grades of gasoline will just average the two octane levels. For example, if you mix 89 and 91 octane fuel at about 50/50, the resulting fuel will have an octane of about 90.

This means that even if you do accidentally mix octane levels, there’s nothing to be worried about. Running a tank of fuel with slightly low octane won’t cause any long-term issues. Of course, this isn’t something you should be doing every time you fill up, but as a one-time thing, there’s not much damage to be done.

Fuel System Service & Repair at Scott’s U-Save

If you’re experiencing problems with your vehicle or its fuel system, trust it to the professionals at Scott’s U-Save! Our ASE-certified technicians have the equipment and training to properly service your vehicle and get it back to driving the way it should be! Call or schedule online today. 

Schedule An Appointment

Whether you're shopping for tires, looking to lift your truck, or need auto repair, Scott's U-Save is here to serve you! Schedule an appointment online or call today!

Get In Touch