What Happens When You Put Regular Gas in a Premium Fuel Car

With gas prices rising, using regular fuel may sound like a tempting proposition since it’s the cheaper option. But why do some car manufacturers recommend using only premium gasoline in their vehicles? How much harm will putting regular gas in a car that requires premium fuel really do?   

Using regular gas for a vehicle that requires premium fuel can affect its performance and cause long-term damage. Cars with forced induction or high compression engines usually require premium fuel to avoid engine knock. Modern cars can adjust timing to avoid knocks, but expect performance to dip.

Keep reading to learn why you should avoid putting regular gas in a vehicle that requires premium fuel. This article will discuss what you gain from premium gasoline, why some cars need it, and what may happen if you don’t heed what the manufacturer recommends.  

We Answered: Can You Mix Regular and Premium Gas In Your Car?

The Difference Between Premium and Regular Gasoline

Let’s start by discussing what the difference is between premium and regular gasoline. Regardless if it’s premium or regular, fuel is a crude oil that’s used to power internal combustion engines.

The key difference between the two fuel grades is their octane ratings:

  • Regular gas has 87 octane.
  • Premium gas has 91 octane (or higher).

Octane ratings represent how much pressure fuel can take before it auto-ignites. The higher the octane rating, the less likely the fuel is to combust spontaneously.  

A common misconception about high-octane fuel is that it can boost performance or clean your engine’s internals, which couldn’t be further from the truth. There’s no harm in putting premium fuel in a car that normally runs on regular gas, but there’s nothing to gain from it, either.  

On the other hand, using regular gasoline in a car that requires premium fuel can negatively affect its performance, and may even cause engine damage. 

Fuel companies may claim that their gas can improve performance or cleanse the engine, but that depends on the additives they use in their products.

Why Some Cars Require Premium Gasoline

Some cars require premium gasoline because they are prone to engine knock, which is that pinging noise you may hear in the engine when you step on the accelerator. Engine knock occurs when the timing of fuel detonation is off.  

The lower octane in regular fuel makes it self detonate more quickly, so premium gasoline is recommended for cars that subject the fuel to more pressure. Vehicles that use forced induction or high-compression engines usually need premium gasoline to run optimally.

Forced Induction Engines

A forced induction engine uses a turbocharger or a supercharger to intensify the amount of air that’s fed into the combustion chamber, increasing the engine’s power output.  

Engines that don’t use forced induction are naturally aspirated, but more vehicles now have turbo-charged engines. Turbocharged engines are becoming more common since they allow smaller engines to achieve comparable power to bigger, naturally aspirated engines that tend to consume more fuel.

High Compression Engines

Another way automakers achieve more power, and better fuel efficiency is by increasing the engine’s compression ratio. A high compression engine can derive more energy from the combustion process, but gasoline heats up the more it’s compressed.  

Since the fuel pressure is higher in forced induction and high compression engines, the gas tends to combust at the wrong time. Hence, such engines require high-octane fuel to avoid spontaneous combustion. When fuel detonates at the wrong time, it sends shockwaves through the engine, which causes that pinging sound known as engine knock.

Knock Sensors and Ignition Timing

Some modern cars have a knock sensor that can detect when knocking is imminent. In these instances, the sensor will send a signal to the ECU (Engine Control Unit), which will retard ignition timing by delaying the firing of the sparkplugs to prevent knock.  

Conversely, when the ignition timing of an engine is advanced, the sparkplugs fire earlier, allowing the engine to achieve peak power. This means the best case scenario in using regular gasoline in a vehicle that requires premium fuel is suppressed engine power due to the altered ignition timing.  

Your Car’s Recommended Fuel

Suppose you’re unsure what fuel your vehicle needs; the recommended fuel type is usually indicated at the back of the gas lid. The minimum octane rating is usually shown for premium-gassed cars.

You can also check your owner’s manual or contact your dealership’s service desk to verify the recommended fuel for your car. Some manufacturers void the car’s warranty if using the incorrect type of fuel damages the engine.  

Keep in mind that some automakers will simply recommend you use premium gas and not require it, even if the vehicle has a forced induction or high compression engine. In these cases, you can safely use regular fuel. However, you may notice a dip in power, and a decrease in fuel efficiency may offset the money you save at the fuel pump.

The Long-Term Effects of Putting Regular Gas in Premium Cars

The immediate effect of putting regular gasoline in a car that runs on premium fuel is engine knocking, or at the very least, a decrease in engine power. Using regular fuel on such a vehicle shouldn’t cause too much harm, as long as it doesn’t happen too often.  

Habitually putting regular gas in a car designed to run on premium fuel can suffer serious damage due to engine knocking.

The rapid release of energy from the prematurely detonated fuel will cause the piston to run counter to the engine’s momentum, making engine knock detrimental to the engine. Damage occurs due to the violent vibrations and thermal strain brought by the sudden influx of heat.  

Frequent or extreme engine knocking can damage crankshaft bearings, pistons, and cylinder walls. Repairs may involve a complete engine overhaul or even an engine swap if the damage is too extensive.

If the engine or one of its main components has suffered significant damage, your car may show one (or more) of the following symptoms:

  • Engine knock occurs more frequently.
  • Blue, white, or black smoke from the exhaust.
  • Fluid leaks around the engine or under the car.
  • Unusual noises like grinding and squealing.
  • A significant dip in fuel efficiency.
  • Increase in oil consumption.
  • Decrease in power.
  • Rough idling.
  • Check engine light on.

There are many causes for engine knock, and low octane fuel is not the only reason. If you continue to experience knocking after filling up with premium gas, bring your vehicle to a trusted service center immediately.

Using Octane Boosters

If your car’s manufacturer requires you to use premium fuel, but you face the dilemma of either using regular gas or stalling because no high-octane fuels are available, go ahead and gas up. However, just put enough fuel in the tank to get you to the nearest gas station with premium gasoline.

Keeping a bottle of octane booster in your car is a good idea for instances where premium gas is hard to find. An octane booster is a liquid additive that contains chemicals like MMT, toluene, and trimethylbenzenes, which work to increase the octane rating of gasoline.  

The K&N Performance Octane Booster (available on Amazon.com) contains special additives that can boost power and clean your fuel injectors, aside from increasing your gasoline’s octane rating. One bottle is formulated to treat a full tank (18 gallons) of gas.  

Final Thoughts

Putting regular gasoline in a car that requires premium fuel will not be harmful if it’s rarely done. Since regular fuel has a lower octane rating, it’s more prone to premature detonation, which causes engine knock. Subjecting any vehicle to extreme and frequent engine knock can damage vital components of a car’s engine.

Premium gasoline has a higher octane rating, which gives it better anti-knocking properties, making it suitable for vehicles with high-pressure engines where knocking is more likely to happen.  

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