If you have just put petrol in a diesel car, the most important thing is simple: do not start the engine. If you have not turned the key yet, you have given yourself the best chance of escaping with a fuel drain instead of a much bigger repair bill.
The AA says that if you put the wrong fuel in your vehicle you should not start it, while RAC says you should leave the engine off, tell the petrol station staff what has happened, put the car in neutral and push it to a safe place if needed, then call for specialist help.
The first five things to do right now
1. Do not start the engine
This is the big one. Petrol does not lubricate a diesel fuel system the way diesel does, so once the wrong fuel is circulated the risk and the cost can climb quickly. Do not try to see if the car will be fine. Do not try to drive home. Do not keep turning the key to test your luck.
2. Tell the forecourt staff straight away
If you are still at the pump, let the petrol station know. They will usually want to help keep things safe and may tell you where the car can be moved if it is blocking a pump.
3. Put the car in neutral and move it only if it is safe
RAC advises moving the vehicle to a safe place if possible. That usually means rolling or pushing it, not starting it. If you are on a slope, in heavy traffic or otherwise stuck, get help rather than trying to improvise.
4. Call a specialist fuel-drain or breakdown service
This is not the moment for DIY optimism. A proper misfuel recovery service can drain the contaminated fuel and flush the system. RAC and the AA both offer wrong-fuel assistance, and many local fuel-drain specialists do too.
5. Keep your receipt and note what happened
Keep the fuel receipt, note roughly how much petrol went in and whether the engine was started. Those details matter if you speak to a recovery service, a garage or your insurer.
What if you already started the engine?
The situation gets more serious, but it is still not a cue to keep driving. Turn the engine off as soon as you realise what has happened and call for recovery.
RAC warns that petrol in a diesel can lead to knocking, smoke, poor acceleration, warning lights, stalling and restart problems. The AA is blunter: the longer a diesel engine runs with petrol in it, the more damage can be caused.
That is why the sensible rule is this:
- not started usually means a better chance of a straightforward drain and flush
- started but not driven far still needs specialist help quickly
- driven until symptoms appear can mean a much uglier bill, because the wrong fuel may already have reached sensitive pump and injector components
Why petrol in a diesel is such a problem
Drivers often hear that putting diesel in a petrol car is bad, so they assume the reverse mistake is similar. It often is not.
Modern diesel systems rely on the fuel itself for lubrication. Petrol is a poorer lubricant, so it can increase wear inside the high-pressure pump and injectors. On older engines, some people got away with small errors more often than they do now. On modern common-rail diesels, gambling on a top-up and a prayer is a reckless idea.
That is why petrol in a diesel is usually treated as the more serious of the two common misfuelling mistakes.
Can you just top it up with diesel and hope for the best?
That is the old pub advice, and it is not good advice for a modern diesel.
The AA and RAC both steer drivers towards specialist draining rather than dilution and hope. Even if the car still seems normal, the point is not whether it will move today. It is whether you are risking expensive damage to the fuel system that arrives later.
If you have put petrol in a diesel car, the safest UK answer is to stop, do not start it and get the tank drained properly.
How much can this mistake cost in the UK?
There is no single national price because the bill depends on what stage you caught the mistake. But the rough shape of the cost is clear enough.
The AA says garages can charge £300 or more for a fuel drain, and that if contaminated fuel has circulated and caused deeper damage, manufacturers may recommend replacement parts that can push the bill into the thousands of pounds, in some cases £5,000 or more.
That is why switching the engine off early matters so much. The gap between an awkward recovery call and a serious diesel-system repair can be huge.
Will breakdown cover or insurance help?
Sometimes, yes, but do not assume every policy covers misfuelling in the same way.
Some breakdown providers sell wrong-fuel assistance as a specific add-on or include it in higher cover levels. Some car insurance policies may help with accidental misfuelling, but terms, excesses and exclusions vary. If you are already stranded, the immediate priority is getting the car recovered safely. The paperwork question comes just after that.
A practical order of play is:
- arrange recovery or a drain service
- ask what will and will not be covered
- check your breakdown policy and insurer once the car is safe
What if you put diesel in a petrol car instead?
That mistake can still cause trouble, but it is usually less common because diesel nozzles are often too large for petrol filler necks. The AA notes that it is generally worse to put petrol in a diesel than diesel in a petrol, but either mistake can still lead to poor running, smoke, misfires and breakdowns.
So the broader rule still stands: if you have used the wrong fuel, stop and get advice before starting the car.
How common is misfuelling?
Embarrassingly common. RAC says it happens around once every three minutes in the UK. So if you have just done it, you are not uniquely cursed. You are just in the club nobody wanted to join.
How to avoid doing it again
A few habits help more than people think:
- pause before lifting the nozzle, especially if you have changed cars recently
- check the label on the pump and the filler flap, not just the colour of the handle
- do not rely on muscle memory if the household has both petrol and diesel cars
- avoid refuelling when you are distracted, on the phone or rushing
- if you drive an unfamiliar hire car or courtesy car, double-check every time
If you are changing cars soon, our guide to whether premium petrol is actually worth paying for in the UK is also a useful refresher on fuel choices that catch drivers out.
Bottom line
If you have put petrol in a diesel car, the cheapest move is usually the least dramatic one: do not start it. Tell the forecourt staff, move the car only if it is safe to do so without starting it, and call a specialist drain or recovery service.
Catch it before the engine runs and you may be looking at an inconvenient but containable fix. Keep driving and the bill can escalate fast.
FAQs
I put petrol in my diesel but have not started it. What now?
Do not start the engine. Tell the petrol station staff, arrange a specialist drain or recovery service, and keep the fuel receipt.
Is petrol in a diesel worse than diesel in a petrol?
Usually, yes. Petrol can reduce lubrication in diesel fuel-system components, which is why the risk of damage is taken so seriously on modern diesels.
Can a diesel survive a small amount of petrol?
Possibly, but that is not a safe rule to rely on. On a modern diesel, the sensible advice is still to stop and get expert help rather than try to dilute it and hope.
How much does a wrong-fuel drain cost in the UK?
The AA says garages can charge £300 or more for a fuel drain. If the engine has been run and parts are damaged, the total can be far higher.
Should I claim on insurance for misfuelling?
Maybe, but check the policy first. Some insurers or breakdown providers help with accidental misfuelling, but cover levels, excesses and exclusions vary.
