Putting the wrong fuel in your car is more common than you might think. Every year, thousands of UK drivers accidentally fill a petrol car with diesel or a diesel car with petrol.
While it can be a stressful mistake, acting quickly can often prevent serious damage and costly repairs.
Here’s exactly what you should do if you’ve misfuelled your vehicle.
For more practical motoring advice, visit our maintenance guidance hub.
What Should You Do After Putting the Wrong Fuel in Your Car?
The most important thing is not to start the engine.
If the incorrect fuel hasn’t yet circulated through the fuel system, the damage can often be limited to draining and flushing the tank.
As soon as you realise you’ve used the wrong fuel:
- Leave the engine switched off.
- Do not turn the ignition on.
- Inform a member of staff at the filling station if necessary.
- If it’s safe to do so, push the vehicle away from the fuel pumps.
- Contact your breakdown provider or a specialist fuel-drain service.
- Check whether your insurance or breakdown cover includes misfuelling assistance.
Avoiding engine start-up is the single best way to minimise repair costs.
What Happens If You Put the Wrong Fuel in Your Car?
The effects depend on which fuel has been used.
Petrol in a Diesel Car
This is the more serious type of misfuelling.
Petrol reduces the lubricating properties that diesel fuel provides to the fuel pump and injectors.
If the engine is started, petrol can damage:
- The fuel pump.
- Fuel injectors.
- Fuel lines.
- The fuel filter.
- The entire fuel system.
Modern common-rail diesel engines are particularly vulnerable, and repairs can become extremely expensive if contaminated fuel circulates through the system.
If you haven’t started the engine, draining and flushing the fuel tank is usually enough to resolve the issue.
Diesel in a Petrol Car
Although generally less damaging than petrol in a diesel vehicle, diesel should never be used in a petrol engine.
Diesel doesn’t ignite in the same way as petrol, which can lead to:
- Difficulty starting.
- Engine misfires.
- Excessive exhaust smoke.
- Engine stalling.
Again, if the engine hasn’t been started, draining and flushing the fuel system will normally prevent lasting damage.
What If You’ve Already Started the Engine?
If you’ve already driven the vehicle or started the engine after misfuelling:
- Pull over safely as soon as possible.
- Switch the engine off immediately.
- Do not attempt to restart it.
- Contact your breakdown provider or a specialist recovery service.
The longer contaminated fuel circulates through the system, the greater the risk of expensive mechanical damage.
Will Insurance Cover Misfuelling?
Some fully comprehensive car insurance policies include accidental misfuelling cover, while others do not.
Depending on your policy, your insurer may help with:
- Fuel draining.
- Recovery costs.
- Repair costs if damage has occurred.
Many breakdown providers also offer dedicated misfuelling assistance as part of their cover.
It’s worth checking both your insurance policy and breakdown membership to see what’s included.
How Can You Avoid Putting the Wrong Fuel in Your Car?
Although mistakes happen, there are several simple ways to reduce the risk:
- Double-check the fuel pump label before filling up.
- Confirm the fuel type shown inside your fuel filler flap.
- Add a reminder sticker inside the fuel flap if you regularly drive multiple vehicles.
- Avoid rushing or filling up when you’re distracted or tired.
- Consider fitting a diesel misfuelling prevention device if you own a diesel vehicle.
Taking a few extra seconds at the pump can save hundreds—or even thousands—of pounds in repair costs.
If you’d like to avoid other expensive motoring mistakes, our guide on driving habits that are secretly damaging your car is well worth reading.
The Bottom Line
Putting the wrong fuel in your car can be alarming, but the key is to stay calm and avoid starting the engine.
In many cases, if the mistake is caught early, a professional fuel drain is all that’s needed to get you safely back on the road.
The sooner you stop driving and arrange assistance, the better the chances of avoiding serious engine damage.
You may also find our guide on what dashboard warning lights really mean helpful for understanding other situations where stopping your vehicle immediately can prevent expensive repairs.
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