Putting diesel in a petrol car is not especially common because the diesel nozzle is generally bigger than the petrol nozzle. Only about 25% of calls to Auto Fuel Fix are for incidents where diesel has been put into a petrol tank.
The below video explains what you should do if you have put diesel in a petrol car and started the engine.
With ANY misfuelling, DO NOT start the car as this will circulate the contaminated fuel.
What damage can it cause?
If you have been unlucky enough to put diesel in a petrol car, you’ll be relieved to know there is usually no serious damage done to your engine. Unlike diesel, which has to be compressed to ignite, petrol is ignited by a spark generated by the spark plugs. If the car is started the diesel will clog up the spark plugs and fuel system, causing the vehicle to misfire, smoke and possibly stop running. After the contaminated fuel has been flushed from the system, the bike or car should start fairly quickly. You will initially see smoke whilst the diesel residue is burnt off, after this the vehicle should run as before the incident.
Signs of diesel in a petrol car
• Engine misfiring
• Engine won’t start
• Engine cuts out
• Smoky exhaust when driving
Two litres of diesel or less
We recommend a full drain for any amount of contamination, but if you have put in 2 litres or less of diesel in a petrol car (less than 5% of a full tank) and then fill up your remaining tank with petrol, there should be no damage caused to your vehicle.
More than two litres of diesel (5%+)
DO NOT START YOUR ENGINE. If you are on the garage forecourt, inform the attendant, push your vehicle to a safe place and call a fuel removal company to drain and flush your fuel tank. Once this has been carried out, you will be fine to start and drive your vehicle without any damage caused.
Turned over the engine (started)
If you have started your car it is recommended to drain off the contaminated fuel and flush the fuel lines with clean petrol. Once this has been done, you should not suffer any further problems and will be fine to fill your car with petrol and drive away without any further work needed.
Driven my car before realising
If you have started your vehicle, STOP driving as soon as it is safe to do so. A full flush of the fuel lines and tank is essential to remove any contaminated fuel. Once this flush has been carried out and the vehicle has cleared the remaining residue diesel from the system, your car should run fine. We do recommend, as an extra precaution, that you change your fuel filter within a few days of the incident, these are a relatively low cost component and are simple to install.
NOTE: Some vehicles may suffer emission problems after a misfuel due to contamination of the sensors and controls. If you have put diesel in a petrol car and experience any problems after the contamination has been removed, seek the advice of a reputable garage or mechanic.
For more information on how a petrol engine works check out this page