Putting the wrong fuel in your car can range from being a minor, fixable issue to causing severe, permanent engine damage. The severity depends primarily on two factors: the type of engine in your car (gasoline or diesel) and the amount of wrong fuel added.
The most common mistake is putting gasoline in a diesel engine. Diesel fuel acts as a lubricant for the high-pressure fuel pump and injectors. Gasoline, which is a solvent, removes this lubrication, leading to metal-on-metal contact that can quickly destroy these expensive components. Gasoline also has a lower ignition point; in a diesel engine that relies on compression for ignition, it can cause violent, uncontrolled combustion, potentially damaging the engine's internals.
The second scenario is putting diesel in a gasoline engine. Diesel fuel is thicker and won't vaporize properly in the gasoline engine's intake system. It can clog the fuel injectors and fuel filter. Because a gasoline engine needs a spark to ignite a precise air-fuel vapor mixture, diesel will likely cause the engine to misfire, smoke excessively, and stall. If you continue to drive, unburned diesel can coat the spark plugs and catalytic converter, ruining these parts.
| Scenario | Primary Risk | Potential Damage Cost (USD) | Immediate Symptom |
|---|
| Gasoline in Diesel Engine | Fuel pump/injector destruction | $5,000 - $10,000+ | Loud knocking, stalling |
| Diesel in Gasoline Engine | Clogged injectors, catalytic converter damage | $1,500 - $4,000+ | Misfiring, white smoke, stalling |
| E85 in non-FlexFuel Gas Engine | Fuel line & injector corrosion over time | $500 - $2,000+ | Check Engine Light, poor performance |
| High-Octane in Car designed for Regular | Minimal to no damage | $0 (often a waste of money) | None |
| Regular in Car requiring Premium | Engine knocking (pre-ignition) | $0 - $3,000+ (if driven long-term) | Pinging sound under acceleration |
The critical action is to NOT START THE ENGINE. If you haven't turned the key, the wrong fuel is contained in the fuel tank. This is a relatively simple and inexpensive fix—a mechanic just needs to drain and flush the tank. However, if you've started and driven the car, you've circulated the contaminated fuel throughout the entire fuel system, dramatically increasing the risk and cost of damage. In this case, shut off the engine immediately, have the car towed to a repair shop, and explain the situation clearly.
