No, you should never put diesel fuel in a petrol (gasoline) car. Doing so, even once, can cause severe and expensive damage to your vehicle's fuel system and engine. The most critical action is to not start the engine. If you've only added diesel and haven't turned the key, the damage is likely contained to the fuel tank and lines, making it a much simpler and cheaper fix. If you start the engine, the diesel will circulate and damage critical components.
The core issue lies in the fundamental differences between the fuels and the engines designed for them. Petrol engines use spark plugs to ignite a fine mist of fuel. Diesel fuel is much oilier and less volatile; it's designed to ignite under high compression in a diesel engine. In a petrol car, diesel won't vaporize properly, clogs the fuel injectors, and provides poor combustion. This can lead to immediate symptoms like heavy smoke from the exhaust, stalling, a complete failure to start, or severe knocking sounds from the engine.
The repair process is methodical. A mechanic must drain and flush the entire fuel system, including the tank, fuel lines, fuel pump, and fuel injectors. They will also need to replace the fuel filter. If the engine was run, the cost escalates significantly as diesel's improper combustion can damage the catalytic converter and oxygen sensors, which are very expensive components.
| Aspect of Damage/Repair | Consequence / Typical Action Required | Estimated Cost Range (USD) |
|---|
| Misfueling Frequency | Common enough that most repair shops have procedures for it. | N/A |
| Primary Immediate Action | Do not start the engine. Push the car to a safe location. | $0 (if you catch it in time) |
| If Engine NOT Started | Full fuel system drain and flush; replace fuel filter. | $200 - $500 |
| If Engine WAS Started | Above, plus potential damage to fuel pump, injectors, catalytic converter, and oxygen sensors. | $1,500 - $5,000+ |
| Fuel Pump Wear | Diesel lacks the lubricity of petrol, causing premature pump failure. | $400 - $800 (part & labor) |
| Catalytic Converter Damage | Unburned diesel clogs and overheats the converter, destroying it. | $1,000 - $2,500+ |
| Fuel Injector Clogging | Diesel's viscosity clogs precision injectors designed for petrol. | $500 - $1,500 (for cleaning/replacement) |
| Towing Cost | Vehicle will likely need to be towed to a repair shop. | $100 - $200 |
