It's reckoned that at least 150,000 drivers put the wrong fuel in their car each year – that’s one every three and a half minutes.
Things have been getting worse in recent years because of the growth in diesel car sales – modern diesels are so quiet it's easy to forget you're driving one. If you put the wrong fuel in your car, don't turn on the ignition or start the engine as this will circulate the contaminated fuel and increase the risk of damage.
The further the contaminated petrol goes in the system, the more expensive the repair
The further the contaminated petrol goes in the system, the more expensive the repair – it can be cheaper in more extreme cases to fit a new engine, which is why repair bills can run into thousands of pounds. Sometimes the fuel pump works as soon as the ignition is switched on, circulating the contaminated fuel – so don’t even switch the ignition system on.
If you put the wrong kind of fuel into an engine, a small amount of contamination shouldn’t cause lasting damage if caught early. The key is to top the tank up with the right kind of fuel before starting the engine. If you've put more than 10% (5 litres in a 50 litre tank) of the incorrect fuel into a tank, you’ll need to drain the tank and refill with the correct fuel, but if you've added less than 10%, top up with the right fuel and run normally.
If in doubt, and you really do need to err on the side of caution here, or you could wreck your car's engine, get the car recovered to a garage for a professional inspection.
For much more information on what to do if you put the wrong fuel in your car, take a look at the comprehensive article on the Auto Fuel Fix website.