Not one metre further

Filling a diesel vehicle with petrol is relatively easy. To put diesel into a petrol tank, on the other hand, requires a bit of force, because the nozzle does not actually fit into the filler neck.

If customers notice their mistake with the wrong fuel, the first rule for both mix-ups applies: do not turn on the ignition. This is the only way there is a chance of still being able to pump out the wrong fuel at a specialist workshop. This costs time and money, but those who start their cars again have far more trouble on their hands:

• Diesel in a petrol engineThe oily diesel fuel clogs the sensitive injection nozzles. In addition, the fuel pump can be damaged, as can the connecting rods, i.e. the connection between the crankshaft and piston, or cylinder heads during the ignition process. Repairing such engine damage takes time and is expensive.

• Petrol in a diesel engine In a diesel engine, the fuel itself takes over part of the lubrication. The constant diesel flow provides an adequate lubricating film, especially for smaller components such as the injection pump. Petrol acts like a solvent in this environment and destroys the protective lubricating film. While modern diesel vehicles have separate oil lubrication, even then the wrong fuel has a negative effect. As petrol has a much lower flash point temperature, the diesel engine may start to “knock”. This can also lead to engine damage.

• No minimum limitIncidentally, there is no minimum limit for incorrectly filled fuel in the event of confusion between petrol and diesel: even if you go to the station with a half-full tank and notice the misfuelling after just a few litres, you should have the fuel pumped out and the fuel system cleaned.Sensor prevents notorious knockingIf the vehicle is designed for super fuel with 98 octane and was filled up with super 95 or with normal petrol (91 octane), the effects are not quite as serious. Modern vehicles often have a so-called knock sensor that detects the quality of the fuel and adjusts the engine management. In practice, this results in less power, but normally no risk to the engine. In vehicles without a corresponding sensor, the fuel can also self-ignite during compression. In this case, uncontrolled ignition and the notorious knocking noise occur - here, too, engine damage cannot be ruled out.

E10  rarely a problem

A call to the manufacturer or a look in the owner's manual will help if you have accidentally filled up with Super E10. Around 90 per cent of all vehicles tolerate the higher bioethanol content without any problems.