Can You Mix Premium and Regular Gas? Let’s Find Out!

If you drive a car with an internal combustion engine, one expense you can’t avoid is refueling. Gas prices are increasing more than ever, so filling your car with regular gasoline may be tempting. But is mixing premium and regular gas a good idea?

Many vehicles can run on premium or regular gas, and mixing them is generally harmless. However, if your car requires high-octane fuel, you should limit mixing premium with regular gas. Doing so may cause a dip in performance, as well as detonation, which could lead to engine damage.

Read on to know the difference between premium and regular gas. This article will discuss the effects of using both types of gasoline and why some vehicles require high octane fuel.

Mixing premium with regular gas.

The Difference Between Regular and Premium Gasoline

Premium and regular fuels are both unleaded crude oils. The main difference between the two gasoline grades is their octane rating, a number used to signify fuel’s ability to cope with improper engine combustion.

Regular gasoline has an octane rating of 87, which is adequate for most cars with naturally aspirated engines. Premium gasoline has an octane rating of 91 or 93 and is required for vehicles with turbocharged or high compression engines.

Mixing Premium and Regular Gas

If your vehicle runs on regular gasoline, refueling with premium gas will not be harmful, nor will your car benefit from it. Some believe that using premium gasoline can increase performance or clean your car’s fuel system, but this is not true. Cars that run on regular gasoline should stick with regular gasoline. 

On the flip side, using regular gasoline could be harmful if your vehicle requires you to refuel with premium gasoline. So, if you’re running low on fuel and only regular gas is available at the gas station, just put enough in to get you to the next gas station with premium fuel.

Mixing regular with premium fuel will cause the octane rating of your fuel to fall below 91 octane. The octane rating will depend on the ratio of regular and premium fuel in your tank.

Octane Boosters

Using an octane booster is one way to protect your engine if you have to use regular gas on an engine that requires premium gasoline. Octane boosters are fuel additives that increase the octane rating of your fuel.

The K&N Performance Octane Booster (available on Amazon) is specially formulated to clean your injectors and other engine components, aside from increasing your fuel’s octane rating.

Why Some Vehicles Require Premium Gasoline

Some manufacturers will recommend using premium gasoline for added performance, while others will require it to prevent damaging the engine. In most cases, premium gasoline is recommended for cars with forced induction or high compression engines.

Forced Induction Engines

Engines that use forced induction or those with a high compression ratio typically require premium gasoline. Forced induction engines use turbochargers or superchargers to increase air intake. Allowing more air into the combustion chamber increases cylinder pressure and compression.

High Compression Engines

There are also (naturally aspirated) engines that don’t have turbos or superchargers with high compression ratios. Engines with high compression ratios have better thermal efficiency and can extract more power from combustion using less fuel. The disadvantage of having a high-compression ratio is an increased tendency for engine knock, resulting from premature gas combustion.

Engine Knock

Another word for engine knock is detonation, which occurs when fuel in the combustion chamber ignites earlier than it should. The combustion timing has to be extremely precise for an engine to achieve optimal performance and efficiency. When premature combustion occurs, the piston disrupts the movement of the crankshaft, causing the engine to lose its momentum.

Engine knock produces a disturbing pinging sound which intensifies as you accelerate. Aside from the annoying sound it makes, engine knock compromises performance and efficiency.

If engine knocking happens frequently, it may also cause severe engine damage due to added friction on the cylinder walls, pistons, and crankshaft bearings.

You may also find interesting the following article: Best Oil Additives to Stop Engine Knocking.

The Advantage of High-Octane Fuel

High octane fuels are more heat resistant and burn slower, significantly decreasing the chance of premature ignition of gas that results in engine knocking. Regular gasoline is more likely to ignite under high compression spontaneously.

If you’re tempted to use regular gasoline because it’s cheaper, just remember that saving a few cents per gallon at the pump might cost you more money down the road if your vehicle requires high-octane fuel.

How to Tell What Type of Fuel to Use on Your Vehicle

Most cars work well with regular gasoline, particularly those with naturally aspirated engines.  Given the increasing demand for more fuel-efficient vehicles, manufacturers use turbocharged engines to make up for smaller displacements.

It would be remiss to say that all high compression engines must run on high octane fuel since there is always an exception to the rule. One such example is the turbocharged Mazda 3 with a high compression SkyActiv engine, where the manufacturer gives a horsepower rating based on the type of fuel you use.

It shows that a car can run on regular gasoline despite using a high compression engine with forced induction. This is because modern vehicles are equipped with ECUs (electronic control unit) that can alter engine timing to accommodate lower octane fuels. But that also doesn’t mean all modern cars with ECUs can use regular gasoline.

The best way to determine what fuel to use is to check the back of your car’s fuel lid. Most cars will have a sticker stating the minimum octane rating required. Check your owner’s manual or consult your dealership if your car doesn’t have a sticker behind the fuel lid.

Mixing Gasoline From Different Brands

Gasoline is essentially the same regardless of which gas station you go to. The difference lies in the quality, quantity, and type of additives each gas company uses.

The Clean Air Act is a federal law that aims to reduce and control air pollution throughout the country. As such, the United States EPA (Environmental Protection Agency) is required to regulate fuels and additives used in motor vehicles.

Fuel additives can clean fuel lines and injectors, improve performance, and lower emissions.  There is a minimum requirement for the amount of additives each fuel company must use in their products. Cheaper brands often use the bare minimum, while more prominent names like Shell and Mobil use more additives.

So, getting your fuel from different gas stations isn’t harmful to your vehicle, but sticking with reputable brands isn’t a bad idea since they usually have better additives.

Final Thoughts

Mixing premium and regular gasoline will not harm if your vehicle doesn’t require premium fuel. Most automobiles requiring premium gasoline have high compression engines prone to detonation or engine knock.

The ECUs of some high compression engines can cope with regular fuel by adjusting their timing. However, you should still limit mixing premium and regular gas if your car manufacturer requires premium gasoline.




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