Putting unleaded (regular) gasoline in a car that requires premium is possible in a pinch, but it's a practice you should avoid for regular use. The primary risk is engine knocking, which can cause long-term damage. Modern cars have knock sensors that can retune the engine to prevent immediate harm, but this comes at the cost of reduced performance and fuel efficiency.
The requirement for premium fuel, typically 91 or higher octane, is tied to your engine's compression ratio. High-performance engines compress the air-fuel mixture more before ignition. Higher octane fuel is more resistant to pre-ignition, or "knocking," which is a damaging, uncontrolled explosion. Using lower octane fuel can cause knocking, forcing the engine's computer to retard the ignition timing. This protects the engine but results in less power and poorer mileage.
If you accidentally fill up with regular, don't panic. For a single tank, it's unlikely to cause catastrophic damage in a modern vehicle. Simply drive gently until you can dilute it with a tank of premium. However, consistently using the wrong fuel can lead to expensive repairs, including damage to the catalytic converter and pistons. Always consult your owner's manual for the manufacturer's specific recommendation.
| Vehicle Model | Recommended Fuel (Octane) | Potential Consequence of Regular Fuel (Long-Term) |
|---|
| BMW M3 | 93 AKI | Reduced power, risk of engine knock, potential sensor damage |
| Mercedes-Benz C63 AMG | 91 AKI | Decreased acceleration, lower fuel economy, ECU protection mode |
| Audi S4 | 91 AKI | Engine knocking under load, possible long-term piston wear |
| Ford Mustang GT (Performance Pack) | 93 AKI | Noticeable power loss, activated knock sensor reducing performance |
| Subaru WRX STI | 91 AKI | Turbocharger inefficiency, increased risk of pre-ignition |
| Genesis G70 3.3T | 93 AKI | Sub-optimal horsepower/torque, engine runs in a protective state |
