Putting the wrong fuel in your car can cause anything from minor performance issues to catastrophic engine damage. The severity depends entirely on the type of mistake. The most common and dangerous error is putting gasoline in a diesel engine, which can destroy the fuel injection pump and injectors within minutes. The reverse—putting diesel in a gasoline engine—will likely prevent the car from starting at all. Using a lower octane gasoline than recommended can lead to engine knocking and potential long-term damage.
If you realize the mistake before starting the car, do not turn on the ignition. This is the most critical step. Starting the engine circulates the wrong fuel, causing immediate harm. Your only solution is to have the vehicle towed to a repair shop where the entire fuel system can be completely drained and flushed.
Using a higher octane fuel than required is generally not harmful, but it's a waste of money, as most modern engines won't see a performance benefit. The real risk comes from using a fuel with too low of an octane rating for your engine's compression.
| Common Fueling Mistake | Likely Consequence | Immediate Action |
|---|
| Gasoline in a Diesel Engine | Severe damage to high-pressure fuel pump and injectors; very expensive repair. | Do not start car; call for a tow. |
| Diesel in a Gasoline Engine | Engine will not start; clogs fuel lines and injectors. | Do not start car; call for a tow. |
| Regular (87 octane) in a car requiring Premium (91+) | Engine knocking (pinging); potential damage to pistons and valves over time. | You can drive, but fill with premium at half-tank. |
| E85 in a non-Flex-Fuel vehicle | Damage to fuel lines, seals, and injectors; engine running poorly or stalling. | Do not drive; system needs draining. |
Always double-check your fuel cap or owner's manual for the correct fuel type. If you make a mistake, acting quickly can save you thousands of dollars in repairs.
