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What to do When You’ve Put the Wrong Type of Fuel in Your Car

Putting the incorrect type of fuel into your vehicle is surprisingly very common. It’s estimated that this problem occurs on average every three and a half minutes to someone in the UK. With the sales of diesel cars increasing year after year, at a time when diesel technology is being developed for race series such as Le Mans cars, it’s never been harder to tell the difference between the two types of fuel. Diesel engines are now typically very quiet and refined, just like a petrol engine.

If you’ve made the cardinal error of putting the wrong type of fuel into your car, remember that the worst thing you can do is turn the ignition on or start the engine. In a modern, fuel injected car, powerful fuel pumps used to supply fuel to the injectors start to pump fuel as soon as the ignition is switched on - you can tell by the faint whirring noise as soon as the key is turned. This can have far-reaching ramifications for your vehicle and cause significant damage. The intricate fuel pump of a diesel engine is not lubricated by oil, but instead uses the fuel itself to keep the pump working in tolerance. Unleaded petrol will act as a solvent on this lubrication, potentially causing significant damage to the workings of the pump; with the various metal parts grinding against each other, and the shavings contaminating both the fuel and the engine. You can usually tell when this has happened when a horrible grinding noise comes from the engine, and the vehicle refuses to start.

Wrong Fuel

Of course, it’s not all bad news. It’s possible to mitigate the damage caused by putting the wrong fuel in the engine by making sure that you don’t start the engine. If you remember this simple advice, and if you’ve put less than 10% of the wrong fuel into the tank, then the car is usually safe to drive as long as you fill it all the way up with the correct fuel. So if you’ve realised your mistake after putting, say, four litres of diesel into a petrol engine, and your tank holds 40 litres or more, filling it all the way up with the correct fuel means that there shouldn’t be any lasting damage to the vehicle. However, if there is more than 10% of the wrong fuel in the car, the tank needs to be drained completely and refilled with the correct fuel.

Always make sure to speak to your nearest garage, preferably one who services your car or other cars made by the same manufacturer, before following the guidelines given in this article. Certain manufacturers will use parts with much less tolerances for this sort of mistreatment than others, so make sure you check first - it could save you thousands of pounds in the long run. It is also worth noting that putting the wrong fuel in your engine can invalidate your warranty, so try to avoid making this potentially costly mistake.