What happens if I use regular gas in a car that requires premium?
In most cases, using regular gasoline in a car that requires premium can cause the engine to knock or ping, leading to reduced power and efficiency. Modern engines will often compensate, but sustained use can increase wear and reduce performance over time.
Premium-required engines are designed to operate with higher-octane fuel that resists premature ignition. When regular gas is used, the vehicle’s computer may retune timing to prevent damage, which typically lowers power output and efficiency. Understanding what this means for your specific car can help you decide whether to switch fuels and how to handle a misfuel situation.
Why some engines demand premium
Engines with high compression ratios, turbochargers, or advanced timing maps rely on higher-octane fuel to prevent premature ignition. When octane is too low, the air-fuel mixture can detonate before the spark plug fires, creating knock. Cars equipped with knock sensors will often retard ignition timing to prevent damage, which can reduce performance and mileage.
Definitions and implications
Premium fuel typically carries a higher octane rating (for example, 91–93 AKI in the U.S.) than regular fuel (often around 87 AKI). In engines labeled “premium required,” that higher octane is essential to preserve peak performance and prevent knock. In engines labeled “premium recommended,” you may notice some performance and efficiency benefits from using premium, but the engine can run on regular with reduced output.
What happens in practice when you use regular in a premium-required engine
Here is a concise look at the main effects you might observe in daily driving.
- Knock or ping sounds under load, such as when accelerating or climbing hills.
- Engine timing may be retarded by the ECU to prevent knock, causing slower acceleration and reduced power.
- Possible drop in fuel economy due to less efficient timing and combustion.
- In some cases, repeated detonation can contribute to long-term wear if the practice is sustained over time.
- Less than optimal performance and smoother running until the next fill with higher-octane fuel.
Even with these effects, most modern vehicles will not suffer immediate catastrophic damage from a single misfuel, but continued use of regular fuel in a premium-required engine is not advised if you want to protect performance and longevity.
If you accidentally filled with regular: what to do next
To minimize potential issues and restore optimal operation, follow these steps after a misfuel occurrence.
- Avoid hard acceleration and high-load driving until you’re back on the correct octane fuel.
- Verify your owner's manual to confirm whether your engine requires premium or simply benefits from it.
- Fill up with premium at your next refueling to restore the intended octane level.
- If you hear persistent knocking, experience noticeable power loss, or the check engine light comes on, have the vehicle inspected by a qualified mechanic.
- In turbocharged or high-performance engines, consider a tank or two of premium to clear any knock-related timing adjustments and confirm normal operation.
Most vehicles will return to normal once they are refueled with the correct octane and driven under normal conditions, but if symptoms persist, professional advice is recommended to rule out any pre-existing issues.
Summary
Premium is essential for many high-compression and turbocharged engines to maintain peak performance and prevent detonation. Using regular fuel can cause knocking, reduced power, and lower fuel efficiency, with potential long-term wear if done repeatedly. If you misfuel, switch back to premium promptly, drive with moderate throttle, and seek mechanical guidance if symptoms remain. For many drivers, the payoff of adhering to the manufacturer’s octane recommendation is smoother operation, better acceleration, and improved longevity of the engine.
