Whoever, out of carelessness at the pump, confuses the nozzle should be aware: misfilling with an unsuitable fuel type generally has unfavorable consequences. At minimum, the engine will stall. In modern diesel vehicles, the delicate injection system can incur costly damage; in gasoline cars, the exhaust aftertreatment can be affected. In principle: the moment you notice the error, stop the fueling immediately. Do not restart the engine and switch off the ignition.
Reasons for misfuelling
Rather than the previously common spatial separation of gasoline and diesel, there are more and more fuel types at a single pump (multi-dispenser).
The gasoline fueling nozzle often fits into diesel filler openings and vice versa.
Modern diesel engines are hard to distinguish from gasoline engines by sound alone (rental cars!).
Advertising stickers on fueling nozzles are often larger than the fuel type labeling.
Strange fuel names like Excellium, Fuel Save, Maxx Motion, Supreme, Ultimate, and V‑Power do not reveal the fuel type.
Product names are easy to confuse. Premium varieties like V‑Power or Ultimate exist for both gasoline and diesel fuels.
Fuel type labeling on the fuel cap is missing or too small.
Drivers are careless or do not know the car (rental cars, carpool, car-sharing, etc.).
Abroad, there are often different designations. For example, at diesel pumps you might see Gasóleo, Nafta, Mazot, and Gazole. To prevent misfuelling, at least a Europe-wide uniform fuel labeling was introduced.
Special caution is advised when refueling from spare cans. These usually have small openings that fit both gasoline and diesel filler necks. In such a case, make sure you are actually filling the correct fuel. When in doubt, use a different can and refuel again.
Fueled with gasoline instead of diesel?
Even with small amounts of wrong fuel in the tank, do not open the driver’s door, as in some models the fuel pump may start. Do not switch on the ignition, do not start the engine and stop/turn off the engine immediately. Always follow the vehicle manufacturer’s instructions (see the manual, for example).
If you have not started the engine or the ignition, draining the gasoline-diesel mixture from the tank may be sufficient in some cases. If the engine has already run, it may be necessary to replace the entire fuel injection system, including high-pressure pump, injectors, fuel lines, and tank. This can cost several thousand francs. In any case, always follow the manufacturer’s instructions.
The repair is mandatory if metal shavings have formed in the fuel system. Even if the engine is still running, components of the high-pressure injection system may already be damaged because gasoline immediately washes away the diesel lubrication film. This is often followed by pump total failure. There is a common misconception that a little gasoline in diesel is harmless, especially in winter. This is no longer true today.
If it is an older diesel vehicle (swirl or precombustion chamber diesel, not direct-injection), a few liters of gasoline in an otherwise diesel-filled tank are usually not harmful.
Did you refuel with diesel instead of gasoline?
Even with small amounts in the tank: Do not open the driver’s door and do not let the engine run. If you notice the misfuel while driving, pull over and turn off the engine as soon as possible. If you can’t find guidance in the manual, contact the vehicle manufacturer’s workshop.
Depending on the engine and the amount of the wrong fuel, you may either continue driving cautiously (and repeatedly top up with the correct fuel) or you may need to have the tank drained. Damage to the fuel injection system and exhaust aftertreatment cannot be ruled out.
Although diesel nozzles at gas stations have a larger diameter than the filler necks on gasoline cars, a misfuel with diesel is possible in many gasoline models. In older vehicles there was often a small flap at the rear of the filler neck to prevent misfueling, but this is usually not the case with current models. The diesel nozzle can often be inserted into the upper part of the filler neck and may even latch there—so a diesel fueling is possible.
Filled up with super instead of premium?
If you filled up with Super instead of Super Plus, you can skip draining the tank; the vehicle’s knock sensor will adjust to the lower octane rating of Super. Very old vehicles, often without catalytic converter and without a knock sensor, should not be asked for high performance. This means you should avoid maximum acceleration, hill climbs, and towing at first, and refill with the correct grade of gasoline.
If you filled up with Super Plus instead of Super
If you’ve filled up with Super Plus instead of Super or Super E10, you don’t need to worry and can continue driving. The only downside: you paid too much at the pump. By the way, the common belief that Super Plus boosts engine power compared to Super is not correct, since most engines can’t make use of the higher quality.
If you fueled with Super E10 instead of Super E5
This is harmless if the vehicle is generally approved for E10. For the vast majority of vehicles, this is the case. The manufacturer provides information. Otherwise, an erroneous fill with E10 can already cause damage. In case of misfueling with E10, you should follow the vehicle manufacturer’s instructions.
According to ADAC experts, it may be sufficient to immediately refill the tank with an ethanol-low fuel (best with Super Plus) to achieve a as uncritical ethanol blend as possible. If you’ve filled the tank to the brim with E10, the fuel may need to be pumped out—depending on the manufacturer’s guidelines.
AdBlue has been filled into the diesel tank?
Filling AdBlue into the diesel tank is easy on vehicles without misfuel protection: for example when using common 5- or 10-liter cans from construction sites or supermarkets with a simple filler pipe. But whether AdBlue was filled into the diesel tank or vice versa, the consequences can be just as expensive as a misfueling with petrol.
If AdBlue has been filled into the tank and the ignition has not yet been switched on, a thorough cleaning of the tank is usually sufficient. If the ignition has been switched on, AdBlue can enter the sensitive fuel injection system. Since AdBlue is highly corrosive to pipes and hoses, this can lead to costly damage. In addition to the tank cleaning, fuel pumps, lines and filters may need to be replaced. The same goes for injectors or injection nozzles.
Depending on the manufacturer and model, the recommendations after a misfueling can differ somewhat. Therefore, read your vehicle’s manual or contact your workshop in case of emergency.
And conversely? Accidentally filling diesel fuel into the AdBlue tank is unlikely: the filler openings (diameter 19.75 mm) do not fit the filler pipes (diesel 25 mm, petrol 21 mm) or the usual reserve-can hoses. If someone misfits here, they should notice quickly that something is wrong.
ADAC tests whether misfuelling is possible
As part of the ADAC car test, all models are checked to see whether misfuelling is possible. It turns out that most diesel models are equipped with a misfuelling protection, whereas petrols often lack this. Negative deviations are listed in the respective car test PDF in the chapter “Everyday practicality.”
By the way: If you put in the wrong fuel, you usually have to pay the costs yourself for draining the fuel or for damage to the fuel system. Car insurance usually does not cover this.
