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What To Do If You Accidentally Put Petrol In A Diesel Car

30 July 2019

Accidentally putting the wrong fuel in your car is one of those nightmare scenarios that everyone fears, but try not to worry if it happens to you - you're certainly not alone.

Statistics show that putting the wrong fuel in your car, also known as misfuelling, happens 400 times a day on average in the UK, meaning some unlucky person somewhere puts the wrong fuel in their car approximately every three minutes!

If you've accidentally put petrol in a diesel car, or vice versa, the most important thing to do is to leave your car switched off and do not attempt to drive it. Here's some useful advice for what to do next:

What Happens When You Put Petrol In A Diesel Car?


If you haven't turned the key and switched the car on, you'll probably be alright - the worst that'll happen is you'll have to bashfully admit your mistake to whoever you call for help.

The real problems start as soon as you turn the key, as that activates the system which will suck the petrol out of the tank and up into your vehicle's fuel lines.

If you turn the engine on and it starts to run, this can cause serious damage to the inner workings of your vehicle.

I Put Petrol In My Diesel Car, What Do I Do?

Either way, if you've realised that you've put the wrong fuel in your car, you'll have to call for an expert to come and help you out. DO NOT, under any circumstances, attempt to drain the fuel tank yourself as doing so can be extremely hazardous to your health.

If you're lucky enough to realise your mistake while you're still at the petrol station, you can leave your car on the forecourt and ask one of the attendants to help you out. If you've been driving for a while and only just realised, pull over in a safe place off the road, turn your car off, put your hazard lights on and call someone for help.

You'll need to ring a recovery service to come and tow your car away to be inspected, drained of the incorrect fuel, and have any damage fixed. It can cost around £200 to have your tank drained and your fuel lines inspected, but if you have breakdown cover  as part of your car insurance policy then most insurers will cover you for misfuelling.

What's The Worst Case Scenario If I Put Petrol In A Diesel Car?


Engines are incredibly complicated pieces of machinery, but modern diesel engines in particular are extremely sensitive in the way they work and putting the wrong fuel into them could in some cases cause your car to be written off.

The chemical properties of petrol can cause major components like the fuel pump - which sends the fuel from the fuel tank into the engine - to break. It can also cause tiny pieces of metal to appear in the fuel system, clogging the car's fuel injection system and potentially damaging the engine itself.

Depending on how bad the damage is and what type of car you drive, you might find that your car could be written off as it could cost more to fix the damage caused by the wrong fuel than the vehicle is worth.

At the very least, putting petrol in your diesel car will require your fuel tank to be emptied and your car's fuel system to be inspected and flushed out with a cleaning agent by a mechanic.

What If I Mixed Petrol And Diesel?

Some people claim that you can mix up to 5% petrol into diesel fuel without any negative effects. That means that if you only put a tiny bit in and then realised your mistake, you'll likely be okay.

However, we'd recommend getting an expert to come and check your vehicle out anyway, or at least to offer you proper advice, as there's never any real way to tell and the risks are too great.

What Happens If You Put Diesel In A Petrol Car?

The majority of misfuelling mishaps - around 95% in fact - happen when petrol is put into a diesel car, and not the other way around. This is because diesel pumps typically have bigger nozzles that don't physically fit into petrol filler tanks.

Of course, it can still happen, but generally putting diesel in a petrol car is less serious than putting petrol in a diesel car. You'll likely gunk up some parts of your engine, which will cause misfires and black smoke to come out of your exhaust, but it usually won't destroy your engine in the same way petrol in a diesel can.

Either way, if you think you've accidentally put the wrong fuel in your car - whether it's petrol or diesel - we recommend keeping the car turned off and seeking professional help.

I Drove My Diesel Car With Petrol In It, Is My Car Ruined?

It's important to remember that even if you didn't realise your mistake and drove off in the car, there's no guarantee that it'll cause lasting damage.

According to experts, many people accidentally misfuel their cars and don't realise until much later when their engines stutter and conk out - sometimes many miles down the road.

However, driving a diesel car with petrol in its tank will cause serious and lasting damage if you continue to drive it. In any case, it's worth calling in the experts and getting your car seen to sooner rather than later -- it's simply not worth the risk otherwise.

Does Putting The Wrong Fuel In Your Car Affect Your Insurance?

This can be a tricky question to answer, as different insurance policies will differ in what they offer cover for. Most standard policies won't cover you for damage caused by mis-fuelling, but you can get special misfuelling cover if you think it's a risk and breakdown cover will sometimes cover the cost of draining, inspecting and cleaning your car's fuel system.

What you might not be covered for, however, is damage caused to your car or its engine as a result of filling it up with the wrong fuel and then driving off on it, particularly if the car is giving off visible signs of being unhealthy yet you continue to drive it anyway.

It's vitally important, therefore, that you know exactly what you are and aren't covered for. A quick phone call to your insurance provider will usually clear those details up, but the golden rule should be that if you have any suspicion that you've put the wrong fuel in your car, stay where you are and call for professional help.

Read More: Is running your car costing you a fortune?