Can you put diesel in a petrol car?

About 150,000 people put the wrong fuel in their car every year in the UK. So, if you’re worrying that it might happen to you, just know that you certainly wouldn’t be the first to do it.

If you’ve recently changed cars, haven’t driven for a while, or you’re driving a rental car, it can be easy to put the wrong fuel in your car. So, is putting diesel in a petrol car or putting petrol in a diesel car even that bad?

If you’re new to driving and want to learn more of the basics, you can check out our blog ‘When to change gears on a manual car?’

Can you put diesel in a petrol car?

The short answer is no, you really should try not to put diesel in a petrol car. Petrol engines use a spark to ignite the fuel as it passes through, but diesel engines don’t. Diesel fuel isn’t as flammable as petrol so it’s unlikely that the fuel will ignite properly in the engine. This can make the engine misfire, or not even start at all.

It isn’t even that likely that you’ll put diesel in a petrol car, even by accident. Diesel fuel nozzles tend to be too big to fit in a petrol car, so you’re likely to notice that something’s up before you even put the fuel in.

What happens if you put diesel in a petrol car?

So what if you actually put diesel in a petrol car? Well, you’re not going to blow up, but you can cause some internal problems with the engine if you can even start the car at all. Diesel essentially covers the spark plugs that ignite the petrol and clogs everything up.

If you even manage to start the car, there are a few things you might expect to see happening if you’ve put diesel in a petrol car:

Your engine could start misfiring
You could see a lot of smoke coming out of the exhaust
Your engine could cut out and not restart

What do I do if I put diesel in my petrol car?

If you realised you put diesel in your petrol car before you left the petrol station, don’t try to drive to a garage. It’s best to put your car in neutral, or even put the key in the ignition, and ask someone to help you push the car out of the way of other drivers. You can then call a recovery company to come and help you out, and it’s probably best to call your insurance company as well. It’s good to check how much your breakdown insurance covers, as it can vary by policy if they’ll pay to get the diesel out of your car.

If you managed to start your car and drive away before you realised that you put diesel in it, it’s best to pull over as soon as it’s safe. Once you’re stopped, you can give the recovery and insurance companies a call.

How do I get diesel out of my petrol car?

Getting diesel out of a petrol car is something you’ll probably want a trained professional to take care of. Basically, they need to drain the whole fuel tank, and then clear the engine and fuel lines. Most recovery companies will be able to do this on-site, and if you haven’t driven the car they might even just give you the right fuel and send you on your way.

If you drive a petrol car after putting diesel in it, they’ll give the engine a more thorough look over before they send you on your way. If there’s any damage, they’ll probably tow your car to a nearby garage to make any repairs you might need.

If you think your car might need a full service whilst you’re at the garage, you can check out our blog ‘How long does a full car service take?’

Can you put petrol in a diesel car?

Again, the short answer is no, you really shouldn’t put petrol in a diesel car. Diesel engines partly use fuel as a lubricant in the engine, but petrol is a solvent. This means it actually dissolves all the lubricant in the engine and causes a lot of friction. This is far from ideal and can cause some damage.

It’s also easier to accidentally put petrol in your diesel car, because the nozzle always fits perfectly. Also not ideal.

What happens if you put petrol in a diesel car?

If you put petrol in a diesel car and start driving, you could have some real issues. The friction caused by the petrol will damage your engine internally. The further you drive, the more damage it can do.

You’re going to want to stop your car as soon as possible if you notice any of these:

Loud knocking sounds while accelerating
Lots of smoke coming from your exhaust
Slow acceleration
Your engine warning light coming on
Your engine stopping and struggling to restart

Damage caused by putting petrol in a diesel engine can be pretty bad. If there’s a lot of damage, you might need new fuel lines, pumps, or filters. You might even need a new fuel tank or a whole new engine. So yeah, not so great.

What do I do if I put petrol in my diesel car?

Basically, this is the same as above. If you realise you’ve put petrol in a diesel car, ideally you shouldn’t start the engine. You can put the car in neutral and push it somewhere safe (ideally with a kind person’s help), then call a recovery company and your insurance.

If you drive a diesel car after putting petrol in it, you’ll probably want to pull over asap. As soon as the car is safely stopped, it’s the time to call recovery and your insurance.

How to get petrol out of a car?

Getting petrol out of a car is the same process as before. The recovery guys should be able to drain all of the petrol and give you the right fuel pretty easily. The only issue you might have is if you drove the car. The recovery service will give the engine a good look, and if there’s damage to your engine, you’ll probably need to go to a garage to get it fixed straight away.

A few final tips…

Whether you put petrol in a diesel car or diesel in a petrol car, it’s not ideal but it’s not the end of the world. If you catch it quickly you’re unlikely to have too much of an issue, but here’s a few things to remember:

If you’re particularly forgetful, you can always write the right kind fuel inside your fuel cap with a permanent marker
If your engine is misfiring or knocking at any point, it’s a good idea to pull over as soon as you can
When you’re buying breakdown cover, it might be worth seeing if you can get misfueling cover, just to give you peace of mind

If you’re interested in learning more about the inner workings of your car, check out our blog ‘How long should a car battery last in the UK?’

Urban Jungle is not a financial advisor and information in this article should not be taken as advice or recommendation.