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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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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