Thread: Unleaded...I can’t believe it happened!

I have a 2016 defender . It has a 70 litre tank
On weekend driving from Melbourne to Sydney I stopped for fuel at Wallan on the Hume highway . Got distracted and dumped some unleaded in before I realised my mistake

On refueling
tank had 25.02 litres of Diesal in it
I put in 22.70 litres of unleaded before realising my stupidity
I then topped up with 22.28 litres of Diesal to fill tank to 70 litres

Garage attendant told me Diesal is heavier than petrol so as long as I keep topped up
it should be ok as the unleaded will stay on the top and the Diesal will get drawn from the bottom

Car drove fine no backfiring or loss of power and engine sounded as normal.

refueled with Diesal as follows

24.17 litres at Glenrowan
17.7 litres at Albury ( also added some Diesal conditioner ((DC))
25.00 litres at Gundagai ...with DC ...small squirt
15.60 litres at Yass with DC ...small squirt
14 litres at Goulburn with Dc ...small squirt


I arrived in Sydney with 3/4 of a tank and the car seems to be running running fine

so some questions ......

1) Do I still have 22.70 litres of unleaded floating on top of my Diesal .....or ( as I suspect ) has it completely mixed in with the Diesal ......and now diluted due to the many top ups

2) should I still drain the tank or should I just keep topping up with Diesal to
completely dilute away the unleaded

3) I have read above that I should at least change the fuel filter


any and all advice suggestions appreciated .

Originally Posted by landoman

I have a 2016 defender . It has a 70 litre tank
On weekend driving from Melbourne to Sydney I stopped for fuel at Wallan on the Hume highway . Got distracted and dumped some unleaded in before I realised my mistake

On refueling
tank had 25.02 litres of Diesal in it
I put in 22.70 litres of unleaded before realising my stupidity
I then topped up with 22.28 litres of Diesal to fill tank to 70 litres

Garage attendant told me Diesal is heavier than petrol so as long as I keep topped up
it should be ok as the unleaded will stay on the top and the Diesal will get drawn from the bottom

Car drove fine no backfiring or loss of power and engine sounded as normal.

refueled with Diesal as follows

24.17 litres at Glenrowan
17.7 litres at Albury ( also added some Diesal conditioner ((DC))
25.00 litres at Gundagai ...with DC ...small squirt
15.60 litres at Yass with DC ...small squirt
14 litres at Goulburn with Dc ...small squirt


I arrived in Sydney with 3/4 of a tank and the car seems to be running running fine

so some questions ......

1) Do I still have 22.70 litres of unleaded floating on top of my Diesal .....or ( as I suspect ) has it completely mixed in with the Diesal ......and now diluted due to the many top ups

2) should I still drain the tank or should I just keep topping up with Diesal to
completely dilute away the unleaded

3) I have read above that I should at least change the fuel filter


any and all advice suggestions appreciated .

It will be perfectly OK, the unleaded will have well and truly mixed with the diesel in the first hour , prob in the first 5 mins, no need at all to keep it topped up. just keep driving as normal.

Originally Posted by spudfan

Suppose this happened in the middle of nowhere, i.e. a couple of your jerry cans had petrol instead of diesel in them, could you throw in a litre of 2 stroke to help with the lubricity of the mix. Could you drive on this mixture until you could find somewhere to top up with diesel?

yes but it depends on the mix, if you can get it started dont stop it and dont ask too much power you'll be ok, petrol burns hotter and faster than diesel so you will be getting detonation which if driven hard will damage pistons, extended driving will up the combustion temps and then the lack of lubricity might be a problem for the injectors, High pressure pump, pressure regulator or the suction control valve.

Originally Posted by landoman

I have a 2016 defender . It has a 70 litre tank
On weekend driving from Melbourne to Sydney I stopped for fuel at Wallan on the Hume highway . Got distracted and dumped some unleaded in before I realised my mistake

On refueling
tank had 25.02 litres of Diesal in it
I put in 22.70 litres of unleaded before realising my stupidity
I then topped up with 22.28 litres of Diesal to fill tank to 70 litres

Garage attendant told me Diesal is heavier than petrol so as long as I keep topped up
it should be ok as the unleaded will stay on the top and the Diesal will get drawn from the bottom

Car drove fine no backfiring or loss of power and engine sounded as normal.

refueled with Diesal as follows

24.17 litres at Glenrowan
17.7 litres at Albury ( also added some Diesal conditioner ((DC))
25.00 litres at Gundagai ...with DC ...small squirt
15.60 litres at Yass with DC ...small squirt
14 litres at Goulburn with Dc ...small squirt


I arrived in Sydney with 3/4 of a tank and the car seems to be running running fine

so some questions ......

1) Do I still have 22.70 litres of unleaded floating on top of my Diesal .....or ( as I suspect ) has it completely mixed in with the Diesal ......and now diluted due to the many top ups

2) should I still drain the tank or should I just keep topping up with Diesal to
completely dilute away the unleaded

3) I have read above that I should at least change the fuel filter


any and all advice suggestions appreciated .

as mentioned earlier the fuel will be mixed thoroughly by now.

as diesels generally have a full flow system with excess returning to the tank at the top, the vehicle will be agitating the fuel from the driving motions theres no way the unleaded will just "sit" on top of the diesel. If you left it to sit long enough and it was warm enough it might fraction out a little.

My guess is that by now youd be at about 5%

using rough and round numbers your initial petrol contamination of the diesel was 33% 22l and 44l of diesel. 66l total capacity. ( I left out the extra bits of diesel, it makes the numbers worse.)

you used 24 of that.. and added 24l of diesel, Lets say you used 21l and added 21l of diesel (works against you the numbers are easier) and had perfect mixing you used 7l of the petrol and 14l of the diesel. so now you have 15l of petrol in 66l of fuel, something like 22% mix

and again 17L you used 3.75l of petrol and the rest diesel, you now have 11.25l of petrol in the tank the rest diesel, 17% mix.


of the next fill of 25l 4.25l would have been petrol burnt so you now have 7l of petrol in the diesel, 10.6% mix

15l of fuel used at 10% is 1.5l leaving you with 5.5l of petrol in the 66l tank thats... 8.3%

14l used at 8.3 is 1.1L (its 1.16 but Im working the numbers against you) so you now have 4.4l in a 66l tank which is 6.6% and give or take a hand full of liters and rounding it means you're under 5% and if you're really worried about it, go run the tank close to dry under light loads and then top it up..

next time you do something like that, feel free to syphon the fuel for me and I'll run it through my donk, Its not going to care about those kind of numbers if I stick it in the long range tank...

Next time just keep filling it up with petrol then ad a few litres of engine oil, give the car a shake and keep on going 🤣🤣

Thanks to all for the advice, much obliged
As reccommended I’ll run out the 3/4 tank and then completely refill with fresh Diesal
Had read somewhere that adding some 2 stroke oil to the contaminated Diesal could be helpful
for lubrication
SHould I do this or not and if so , how much 2 stroke oil should I add to 3/4 of a 70 litre tank?