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What Happens If I Put the Wrong Fuel in My Car?

We’ve all been there when filling up our car at the petrol station. You’ve already stuck the nozzle in and started filling your tank with fuel, then a sudden thought hits you - did you grab the right nozzle from the pump? You spin round in a panic, only to realise that of course you chose the right one. But what happens if you do actually put the wrong fuel in your car?

I’d never do that!

It might seem like something you’d never do, but according to the AA, around 133,000 motorists put the wrong fuel in their car every year. Whether it’s a lapse in concentration, you’re in a rush, you’ve hired an unfamiliar model or have just switched from petrol to diesel, it’s clearly a common mistake.

What should I do if I fill up with the wrong fuel?

If you realise that you’ve put the wrong fuel in your car, it’s really important that you don’t start the engine. In fact, don’t even put the key in the ignition. Stick your car in neutral and get some help pushing it to a safe place when you can wait for proper assistance. Call either your breakdown company or a mechanic that can help you drain your fuel tank, before filling it up with the correct juice.

What damage can it do?

Starting the engine when you’ve got mixed fuel in the tank can cause permanent damage to your engine that costs a lot to repair. Putting petrol into a diesel tank causes more damage than vice versa. Unfortunately, it’s usually easier to make the mistake of doing that, as petrol nozzles fit into most modern diesel filter necks. 

It hurts your engine because the petrol acts as a solvent, reducing the lubrication that diesel brings to the fuel pump to help it work. The petrol means there’s more friction between parts of your engine, and the more mixed fuel that’s pumped around it, the more damage is done. 

Do certain engines get damaged more than others?

Common rail diesel engines, also known as HDi, are at greater risk of damage from the wrong fuel. If you start the engine and do a lot of harm to your car, you could be looking at new fuel pumps, pipes injectors, a replacement fuel tank, or even a whole new engine as a worst-case scenario.

Does diesel still damage a petrol engine?

Your petrol car ignites fuel through spark plugs, while diesel must be compressed to ignite. If you add diesel to a petrol car, the likeliest thing to happen is that you’ll clog up the spark plugs and fuel system, and the car will either cut out or won’t be able to start at all. You’ll still need to drain the tank and may need to replace the spark plugs, but it’s usually not as disastrous as the damage petrol can cause to a diesel engine.

What can I do to stop myself misfuelling?

Aside from the obvious things like making sure you’re paying attention and trying not to rush when you’re at the petrol station, there are things you could do to avoid filling up with the wrong fuel. If you’ve just changed your car and it uses different fuel, leave yourself some reminders in the car to help jog your memory. Or if you drive a diesel, there are little devices you can get that stop you inserting a narrower petrol nozzle into your filler neck. 


If the worst does happen, contact Inchcape today and our expert servicing teams will tell you how we can help.