Petrol in Diesel

Petrol in a Diesel Engine

Petrol in a Diesel Engine

If you have put unleaded in petrol in your diesel car then you need to think very carefully about your next step. The more petrol you have put in, and the newer the car, the more trouble you are in!

If you have a very old diesel, and in particular a diesel engine that is not a common rail (Hdi, or THdi), and you have only put a small amount of petrol in the diesel tank then you may well get away with your mistake. In these circumstances if you have put less than 5 litres of unleaded petrol in the diesel tank then you can get away with filling up the tank to the top with diesel and drive off with little problem.

If you have accidentally put more than 5 litres of unleaded petrol in a diesel car, or if you have a modern car then you need to be a lot more careful. If this is the case then under no circumstances should you start the engine, in fact its best if you don’t even use your keyfob to unlock the car as this can start the fuel pump. If you have put petrol in your diesel you need to call for help, someone like the AA or the RAC will be able to sort you out. You usually don’t even have to be a member, but you will of course be charged.

If you are lucky it may be possible to completely drain the diesel fuel tank that has been accidentally contaminated with petrol, and then simply fill it up again. You should probably consider getting your engine seals and filters changed to be on the safe side. If you have started the car, or have a ultra modern high performance diesel then you may need to have parts of the engine such as the fuel pump stripped down and cleaned.

In the very worst instances you may need parts of the engine replaced, or even a new engine.

Accidentally putting petrol in diesel is usually not covered by your insurance, and could invalidate your cars warranty, so it could be very expensive.

What does accidentally putting petrol in diesel actually do?

Petrol is a particularly good solvent and it acts to reduce the amount of lubrication in the engine, and so a diesel engine filled with petrol can literally shred itself from the inside. The most vulnerable is the diesel fuel pump which has to pump the fuel to extremely high pressures. If petrol is present in the diesel then this fuel pump will grind metal against metal, damaging the pump itself and causing all sorts of problems further down stream of the pump.

The seals in the engine will also be affected, they will get degraded by the petrol in the diesel and could leak or have other lubrication problems.

How often is petrol accidentally put in diesel?

Accidentally putting unleaded petrol in diesel is surprisingly common, with some websites claiming that it happens more than 400 times a day in the UK. One of the problems is that modern diesel cars run a lot smoother and quieter than they used to and so people often simply forget that they are driving a diesel, especially if they have borrowed or hired the car. Another problem is that petrol fillers will usually fit into the diesel filler cap as the petrol filler nozzles have a smaller diameter than the diesel filler nozzles. One final issue that the filler nozzles used to be colour coded green for unleaded, black for diesel and red for leaded, but nowadays they tend to be coloured used the brands colours instead.

How can I avoid accidentally putting petrol in a diesel tank?

Your first line of defence is to put a label on the filer cap or even next to your fuel gauge on the dashboard. This should act as a reminder to you when you go to fill up the tank and hopefully prevent accidental misfuelling. If you don’t like the idea of labels, or think that this still won’t help you then you can look for 3rd party filler caps on the market which physically prevent you from putting a petrol filler nozzle in through the filler cap. Finally companies such as Ford are now fitting special caps as standard which prevent you from accidentally using the wrong fuel.

With diesel cars gaining in popularity the number of people of accidentally putting petrol in diesel engines is going to grow and grow.

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