Can You Mix Premium and Regular Gas – What Happens If You Mix

Can You Mix Premium and Regular Gas1
Read Time:6 Minute, 47 Second

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.

What Is Premium Gas?

Premium gasoline is a type of higher octane fuel. It is frequently used in high-performance vehicles. The octane level refers to how much compression the gasoline can withstand before igniting.

High-performance cars tend to have powerful engines. With higher compression ratios in these engines, they require a higher octane gas to work properly. This does not mean that regular gas will impact performance, though.

What Is Regular Gas?

Regular gas, also called unleaded gas, is the most commonly used type of fuel in cars. “Regular” used to refer to leaded gasoline. However, lead has been banned from gasoline in most countries; therefore, regular gas refers mostly to unleaded gas with a lower octane level.

What Happens If You Put Regular 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.

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

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.

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!

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!

Mixing premium gas with regular gas probably won’t hurt anything for the most part. It depends on your vehicle really. If your vehicle is a sedan that requires regular gas, the blend of premium and regular gas should have plenty of octane and detergent to spare.

It might even get a bit of better mileage or run a little bit better if you’re lucky. However, if your ride requires premium gas instead of regular gas, the blend can actually reduce octane and make your vehicle run less efficiently compared to simply using pure premium gas.

More about Mixing Premium Gas with Regular Gas

  • The Risk of Pinging: The majority of modern cars include computer controls to protect itself and to drive safely, so mixed gas should have little effect. However, older cars without these car computers might start pinging or the sound when the air/fuel mixture is igniting too quickly as caused by low-octane gas or a poorly timed motor. The solution to this is to top off the vehicle with premium gas until the octane is high enough to eradicate the sound.
  • Mid-Grade Gas and Unleaded Mixing: For regular gas cars that benefit instead of suffer from mixed gases, you can possibly save more by using mid-grade gas instead of mixing premium and regular gas together in order to get to the same octane level. Furthermore, it’s actually fine to combine different octane levels of gas as long as they’re both of the unleaded variety. You risk car damage or more if you use “leaded” gasoline mixtures on your vehicle.
  • Regular Gas Mixed with E85 Fuel: When you mix E85 fuel with regular gas, you’re diluting the high-octane rating of E85. To be more specific, there’s higher octane in ethanol compared to standard gas. As such, the more gas you add to the E85 the lower its octane becomes, which defeats the purpose of getting more octane. Because E30 gas isn’t available at pumps, you have to blend E85 gas with 93 octane gas to receive the 70% gasoline and 30% ethanol ratio that’s ideal for your vehicle.
  • To Mix or Not to Mix: Some car owners mix, for example, 87s and 94s together for their Mercedes that requires 91-octane gas when it gets half-full. The question here is, “Is mixing regular gas with high-octane gas worth it?” Car experts claim that it’s no real help finance-wise or performance-wise when you mix super premium gas with regular gas. Run one octane or another and don’t bother wasting money mixing gases.

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 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.

Can You Mix Premium and Regular Gas

Is It Bad To Mix Premium And Regular Gas?

In older vehicles, mixing regular and premium gas would’ve caused serious engine knocking, and would have happened rapidly. Nowadays, engines are more adaptable to the variety. Is it bad to mix premium and regular gas? Actually, not always. If your car requires premium to run smoothly, but you aren’t able to find a station with premium gasoline, it won’t hurt to top off with regular gasoline. You do want to avoid running on regular gasoline for extended periods of time.

There are a variety of reasons your vehicle may need premium gas. Mixing regular and premium gas may be bad if you have a turbocharged engine, which requires higher octane fuels to operate properly, or maybe you opted for a high-performance car with a high-strung engine that operates with tight tolerances

How Do You Tell Which Type Of Fuel Your Car Uses?

You should consult your car manual if you are uncertain whether your car takes premium fuel or regular gas. If you have misplaced the manual, there should be a sticker inside the fuel door (the flap you open to get to the fuel cap and fuel tank). This sticker should indicate whether your car takes diesel or petrol, and also the octane rating required in the case of petrol.


It is not recommended that you switch between gas types. Older cars that require higher octane fuels may instantly experience “knocking” when filled with lower octane gas. As mentioned already, more modern engines that require premium gas should be able to detect the octane fuel levels and adjust accordingly. So it will come down to the age of your premium gas car.

Cars that require regular gas are also unlikely to benefit from the use of premium gas. However, if you are in a pinch and it is the only fuel type available, you can fill up with high-octane fuel.

Related Posts

Average Rating

5 Star
4 Star
3 Star
2 Star
1 Star

Leave a Reply

Your email address will not be published.

Pin It on Pinterest