Misfuelling: Mistaking petrol for diesel—what to do?

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If you fill up out of habit but drive a different vehicle at short notice, it can happen that you fill up with the wrong type of fuel. Here we explain what you should do immediately if you are confused between petrol and diesel.

It is impossible to fill up with the wrong fuel at modern petrol stations, as the diesel nozzle is thicker and does not fit into the narrow tank opening of a petrol car. If this happens anyway for other reasons, we can help here.

Misfuelling: diesel and petrol mixed up – what should I do?
If you notice that you have mixed up diesel and petrol and are filling up with the wrong fuel, first stop refuelling as quickly as possible and remove the nozzle. The next step is to prevent the incorrectly refuelled fuel from entering other systems in the car:

Leave the engine and ignition off.
If possible, keep the vehicle door closed. Modern cars activate the fuel feed pump of the injection system as soon as the vehicle door is opened.
・If you are still or already back in the car, call the petrol station and explain that you have filled up with the wrong fuel and why you don’t want to get out of the vehicle. Locate your position on Google Maps, for example. You can usually tap on the petrol station, and the corresponding phone number will be displayed there.
Otherwise, you can climb out of the window, but be careful not to damage anything. It’s best to take off your shoes first. Alternatively, you can call a passer-by for help, who will inform the petrol station attendant or staff about your situation.
If you have already set off, stop the vehicle immediately at the next best place. If this happens on a motorway, drive onto the hard shoulder first, switch on the hazard warning lights, and leave the car on the side facing away from the motorway. Do not cross the highway under any circumstances! There is a danger to life. Put on your safety waistcoat, take the warning triangle, jump over the crash barrier on your side and walk back at least 150 metres (300 metres is better) to set up the warning triangle there. As a guide: The distance between two delineators is 50 metres. You should, therefore, walk at least 3 to 6 delineators to set up the warning triangle. Road users will see your warning triangle on bends and hills too late. You should then place it in front of the bend or hill. If your car endangers traffic, call the police on 110 as soon as possible. Otherwise, call a breakdown service of your choice.

Car symptoms after misfuelling
If you have refuelled incorrectly, the car may show the following symptoms: The engine makes strange noises and stalls. This can severely damage the injection system of modern diesel vehicles.

The most important symptoms are:

・The car makes unusual noises (engine runs out of round, jerks, stutters, or nails).

・The engine does not deliver any power to the road.

・The engine warning light comes on or flashes.

・There is heavy and/or black smoke coming from the exhaust.

・The engine stops.

How long does a car run on the wrong fuel?
Not very long:

・If you have filled up a petrol car with diesel, it will usually still start because residual petrol is still getting into the cylinders through the pipes. However, the spark plugs can no longer ignite the diesel at a certain point, causing the engine to stall. Even if the engine continues to run with heavy knocking, this can quickly result in a total loss.

・If you fill up diesel with petrol, the engine will be severely damaged. Diesel is greasier than petrol and usually lubricates the car’s high-pressure pumps. Petrol does not do this in a diesel engine. This can cause the pump to block and/or the timing belt or timing chain to break, resulting in total engine damage. In the worst-case scenario, the engine, timing belt/timing chain, catalytic converter, injection system, high-pressure pump, injectors, fuel lines and tank would have to be replaced. This is then very expensive.

Incorrect refuelling: the costs
If you have already started the engine with incorrectly refuelled fuel, it must be pumped out of the tank, engine and the associated lines. In addition, the engine parts must be cleaned and inspected for damage. Never pump out the fuel yourself. There is a risk of explosion! It is better to have this done by a professional workshop.

Towing service in the garage

If you have also damaged cylinder heads or the fuel pump due to the mishap, this can cost 2,500 to 3,500 euros, depending on your car model. A new engine alone costs around 1,000 to 3,000 euros.

Quick guide: Incorrect refuelling
・Leave the car switched off! If you have already started it, pull over and switch off the engine and ignition!

・If possible, keep the vehicle door closed so as not to activate the booster pump.

・Turn to the petrol station staff or ask passers-by for help if you are stuck in the car.

・Contact a breakdown service to tow the vehicle and take it to the nearest garage.

・The engine and all associated components must be drained of the wrong fuel and cleaned.

・Depending on if the car was started and/or driven with the wrong fuel, costs of 500 to 3,500 euros can be incurred. In the worst case, it is a total loss.