Accidentally put a bit of unleaded in my diesel car, does it matter?

Posted 13th Jan 2015

A couple of weeks ago I went to fill up my diesel car (fuel warning light had been on a while so low on fuel), and for some reason started filling with super unleaded! I had only put in about 90 pence worth when I realised so not a lot.
Not being one to worry too much about anything I then topped up with about £40 worth of diesel in the hope it would all get mixed up and be fine.
And the car was fine and has been since. But someone has mentioned to me it could still be an issue, potentially affecting parts in the engine, or if the unleaded doesn't mix and sits at the top, or bottom of the tank.

Is the small amount of petrol anything to worry about?

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4th Nov 2019

What to do if wrong fuel in car

Despite petrol stations’ best efforts to colour code each type of fuel stand, putting the wrong fuel in ythe car is something that a lot of drivers are bound to experience at some point in their lives. How you should respond to this depends on the amount you’ve filled up your tank. Attempting to carry on like normal could have grave consequences for your car, so read this short guide before trying to resolve the situation.

Putting unleaded in a diesel engine – What to do if you’ve completely filled your tank

If you’ve filled your diesel engine completely with petrol, then you’ll need to act with caution. Do not turn your ignition under any circumstances. Completely remove your keys from the ignition,, ask the petrol station staff to help you push your car to a safe location and call your breakdown cover (like the AA) to help you. If you try and drive away, the likelihood is that you’ll break your engine, so don’t attempt to carry on like nothing has happened. The price could be having to get a brand new engine or worse, a brand new car.

I put 2 litres of petrol in a diesel engine! What do I do?

If you have a diesel car and only accidently poured a little petrol into the diesel engine, then there’s no great cause for alarm. With the average car fuel tank having a capacity of around 50 litres, you can fill up the rest of your tank with diesel and still be okay. This is even something that drivers do in cold countries to keep their engines functioning smoothly – although it’s not recommended in the UK’s milder climate. If you want to be completely safe, then don’t turn the ignition and call your breakdown cover.

How to drain wrong fuel from car

It’s generally recommended to have your breakdown cover take care of draining the wrong fuel from your car. However, if you have some mechanical experience, you may be able to do this yourself.

To do this, you’ll need to have or purchase a siphon tube with a hand pump, a screwdriver with a long, thin body, and a fuel storage can. When you have these, do the following:

Feed the siphon pump tubing into the fuel tank – Open up your fuel tank door and slowly insert one end of your siphon pump down into the fuel tank. Do this in very small increments to prevent the tube from kinking. Your car may have a small metal door designed to prevent fuel siphoning. Use your screwdriver to push this door open.
Pump the fuel into the tank – Feed the other end of the tube into your fuel storage tank. Operate the hand pump until the fuel begins to flow through the tube. If you’ve completely filled your tank, this may take some time and effort. Continue until your fuel gauge reads empty.
Dispose of or store the fuel – Dispose of the fuel properly (don’t simply pour it down a drain) or store it for later use.

Is putting the wrong fuel in your car covered by insurance?

Different car insurance providers have different policies when it comes to misfuelling. While many do cover breakdowns caused by misfuelling, others don’t cover this whatsoever and expect this to be covered by your breakdown cover. Regardless of the insurance company you’re with, do not drive-off knowing that you’ve filled up your car with the wrong fuel. Your insurance will immediately deny your claim if you do so.

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42 Comments

13th Jan 2015

I'd have filled it all the way to be sure, but i'm sure it'll be fine.

13th Jan 2015

I have done this a few times my car being diesel and my wife's being petrol, never had any probs but I have always filled up after I put a bit of the wrong fuel in. last time I put £5 of petrol in my diesel then had to put £65 worth of diesel in, much to my dissatisfaction.

13th Jan 2015

Write off

deleted34178

13th Jan 2015

It will not do any harm, in fact in very low temperatures, it can actually help, it helps to stop the diesel from freezing.

13th Jan 2015

jonherb
Write off

. LOL you have helped the nerves

13th Jan 2015

You'll be fine.

13th Jan 2015

what car do you have?

EliTom

13th Jan 2015

For 90p worth you should be fine,like someone else said adding petrol to diesel stops it from freezing which is what some people do in their lawn mowers but really only useful if you live in the artic you may notice abit of white smoke when you get to the bottom of the tank but I'd try and keep as much diesel in it for awhile now

13th Jan 2015

knowing which car is important!

yes it's only about 2.5% mix but modern common rail diesel engines rely very much on the lubrication properties of diesel and this is removed by petrol.

so OP - which car? then I can give you some better / more informed information ..... rather than just you will eb OK / write off !

EliTom

13th Jan 2015

omg sell the car.
the engine will now only last 900,000 miles rather than the 999,999 miles

13th Jan 2015

if older car it will help clean you injectors so just fill it right up with diesel .

13th Jan 2015

it will be fine.

13th Jan 2015

in norway they add petrol to diesel. its called winter diesel.so you car will be ok

13th Jan 2015

I done the same and was petrified to tell my husband as he is a mechanical engineer and was expecting a lecture but he said as it was such a small amount doesn't do any harm and said they often do it in colder climates anyway!

13th Jan 2015

elitom
knowing which car is important!yes it's only about 2.5% mix but modern … knowing which car is important!yes it's only about 2.5% mix but modern common rail diesel engines rely very much on the lubrication properties of diesel and this is removed by petrol.so OP - which car? then I can give you some better / more informed information ..... rather than just you will eb OK / write off !EliTom

2005 Astra 1.9 CDTI

13th Jan 2015

Thanks all, sounds like nothing to worry about then

13th Jan 2015

Dantooine
Thanks all, sounds like nothing to worry about then

hmm maybe ...

astra 1.9 cdti is a high pressure common rail diesel injection system - Bosch high pressure fuel pump - it is a version of Fiat's uniJet Turbo Diesel .... one of the first common rail diesel engines.

the problem here is that the high pressure fuel pump runs with extremely tight tolerances and lubrication is provided by the oils in the diesel fuel. Petrol trips these oils out of the diesel for want of a better terminology - try putting a bit of diesel on your hand and feel how oily it feels - now wipe your hand with a bit of petrol and note that the oily feeling has gone. Even running a high pressure fuel pump with a small amount of petrol can cause serious wear in the fuel pump and hence a failure at a later date. The same can happen if you run the car out of fuel - the pump will run dry for a short time - this is enough to cause permanent damage.

So it kind of pot luck really - you maybe lucky or you may have cause some premature / serious wear in the high pressure fuel pump.

Your call really - but yes there is some risk.

EliTom

13th Jan 2015

Not that I've ever done it, but what about the other way around, a small amount of Diesel in a Petrol engined car?

13th Jan 2015

if it still drives then no problem isn't it?

13th Jan 2015

darkovo
Not that I've ever done it, but what about the other way around, a small … Not that I've ever done it, but what about the other way around, a small amount of Diesel in a Petrol engined car?

in theory not quite as bad, the diesel will wax up injectors, but petrol will in theory wash the wax away

BUT unless it is a very old car it is neigh on impossible due to the smaller filler neck on a petrol car fuel tank. You would really have to put diesel into a unleaded fuel can then put it in the car tank ......

on very modern cars with direct injection gasoline engines the diesel will most likely clog the filters / injectors and the car will not run. if it does run then damage will occur to the catalyst and lamda / oxygen sensor - both are expensive to replace !

No real experience of this scenario because it is near impossible to re-create

EliTom

Edited by: "elitom" 13th Jan 2015

13th Jan 2015

mutley1
if it still drives then no problem isn't it?

read post number 17

EliTom

13th Jan 2015

I used work for a fuel company and we were always told tell the customer to keep the tank topped up for a while to dilute the petrol and its fine. 90p worth though, id say ur alright. diesel engines are hardy.
diesel in a petrol engine is a disaster though.

13th Jan 2015

it will be fine but would suggest you pop into your local auto accessory shop or fuel station and by a bottle of diesel fuel addative and pop that in the tank.

deleted242925

13th Jan 2015

jonherb
Write off

Not only a write off but huge fire hazard that will go up in a ball of flames while you're driving along the motorway. Wouldn't worry about it, if it had been the other way round then maybe but dont forget next time

My fiesta and newer model fords wont let you put the wrong fuel in, on the diesel will fit in mine and petrol in my other halfs car thankfully.

13th Jan 2015

deiseaj058
I used work for a fuel company and we were always told tell the customer … I used work for a fuel company and we were always told tell the customer to keep the tank topped up for a while to dilute the petrol and its fine. 90p worth though, id say ur alright. diesel engines are hardy. diesel in a petrol engine is a disaster though.

Never did my xr3 any harm , had the car a good few years after filling it with diesel with no problems

13th Jan 2015

snoopy18
Never did my xr3 any harm , had the car a good few years after filling it … Never did my xr3 any harm , had the car a good few years after filling it with diesel with no problems

and the same logic holds true for modern engines?

EliTom

13th Jan 2015

I put £20 worth of petrol in the wifes diesel focus the night before our wedding. It was midnight the night before our wedding we were driving back to her hotel after a family party and her car was low on deisel. I got out to fill her up with £20. my cars a petrol car so didnt think about it. We got about half a mile down the road and the car started juddering badly so we pulled over and she asked me what fuel id put in. So after a telling off we phoned the RAC for them to come to our rescue. They dont cover wrong fuel so it cost us £300 to get the car flushed out and the fuel system bled. 2 hours later the car was luckily running fine again. If we had of been with green flag it would of been free. We also lost the £20 of fuel and what was in the tank and also had to pay for the fuel he put in the car to get to the petrol station.

After that we still got married and while we were wating for the RAC we updated my speech for the following day

13th Jan 2015

No problem with that small amount

deleted34178

13th Jan 2015

elitom
and the same logic holds true for modern engines?EliTom

Stop scaremongering, the small amount involved will do no harm.

13th Jan 2015

This ^^^

If it's fine now then it'll stay fine. I'd keep topping it up with diesel though to keep reducing the (already small) percentage of petrol.

14th Jan 2015

With 90pence worth it should be fine. Had you topped up a few litres you would have needed to drain the fuel tank, but as other have said, just keep topping up with diesel and you should be fine

14th Jan 2015

Cheers all, I'm not worrying now. May pop into my local garage to ask their opinion

14th Jan 2015

Dantooine
Cheers all, I'm not worrying now. May pop into my local garage to ask … Cheers all, I'm not worrying now. May pop into my local garage to ask their opinion

Wouldn't even do that as depending on garage will see you coming as its work

22nd Dec 2015

Just put in 6.2 litres of unleaded petrol into a diesal mini bus. When realised the error topped up with 51.94 of diesal. Should we worry???

22nd Dec 2015

elitom
in theory not quite as bad, the diesel will wax up injectors, but petrol … in theory not quite as bad, the diesel will wax up injectors, but petrol will in theory wash the wax awayBUT unless it is a very old car it is neigh on impossible due to the smaller filler neck on a petrol car fuel tank. You would really have to put diesel into a unleaded fuel can then put it in the car tank ......on very modern cars with direct injection gasoline engines the diesel will most likely clog the filters / injectors and the car will not run. if it does run then damage will occur to the catalyst and lamda / oxygen sensor - both are expensive to replace !No real experience of this scenario because it is near impossible to re-createEliTom

Neigh on impossible means there's always a possibility....:{

birminghammail.co.uk/new…860. oO

22nd Dec 2015

Mazscl2016
Just put in 6.2 litres of unleaded petrol into a diesal mini bus. When … Just put in 6.2 litres of unleaded petrol into a diesal mini bus. When realised the error topped up with 51.94 of diesal. Should we worry???

Drive it as normal and once the fuel gauge is half way just fill it up again to the top.

22nd Dec 2015

90p worth is about a thimbleful isn't it?

18th Apr 2019

Hi guys I think I might of had the same problem only if I did then I believe I put about £10 worth of petrol into a deisel engine. I only ask because as I left work tonight I had a plume of white smoke come out of my exhaust. The car drove okay once I got going but im worried it might knacker the engine.

22nd Apr 2019

To Elitom -
What about petrol in the diesel of a Renault Megane diesel, 2011?

5th Dec 2019

Hi Elitom, On my way to work this morning I mistakenly put in 20 pounds petrol in a diesel engine vauxhall Insignia. Am a bit worried that I might have damaged the engine. I don't know if u ve a suggestion for me Pls.

Edited by: "Ponkey" 5th Dec 2019