Putting the wrong fuel in is more common than people think — and what you do in the next few minutes matters. The biggest mistake is trying to “see if it’ll be alright”, because that’s what causes the expensive damage.
If you’ve put the wrong fuel in, do this immediately
Do not start the engine. If you haven’t turned the key/pressed start yet, you may have avoided damage.
If the engine is running, switch it off as soon as it’s safe. Don’t drive it.
Move the car only if it can be moved safely without starting it. If forecourt staff can help push it to a safe spot, that’s ideal.
Call for help and explain exactly what happened:
Which fuel went in (petrol or diesel)
Roughly how much
Whether the engine was started
Vehicle make/model (especially if it’s diesel)
Why you shouldn’t start it
Petrol in a diesel can damage the fuel pump and injectors because diesel systems rely on fuel for lubrication.
Diesel in a petrol can clog fuel lines and prevent proper ignition.
Either way, keeping the engine off is the safest way to avoid turning a simple mistake into a major repair bill.
What happens next (in plain English)
In most cases, the fix is to remove the contaminated fuel and get clean fuel back into the system. What’s needed depends on what was added, how much, and whether the engine was started.
If you did not start the engine: it’s often a straightforward drain/flush and refill.
If you started or drove the car: the wrong fuel may have circulated, which can increase the amount of work required.
How to prevent misfuelling next time
A few simple habits reduce the chances of it happening again:
Pause and read the pump label before you lift the nozzle.
If you’ve recently changed vehicle (petrol ↔ diesel), add a small reminder (dash note/keyring tag) for the first few weeks.
Avoid refuelling when you’re rushed, stressed, hungry, or distracted.
If you drive a diesel and worry about misfuelling, you can buy a filler-neck guard that helps prevent a petrol nozzle being inserted.
Quick checklist before you call
If you can, have this info ready:
Location (petrol station + pump number if relevant)
Vehicle make/model
What fuel went in and approx amount
Whether the engine was started or driven
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