Putting the wrong fuel in the car, gasoline uses diesel as a relatively easy mistake. It is also effortless to prevent this error from resulting in a visit to the workshop of thousands of euros.

Mixing gasoline and diesel itself is not the end of the world, as long as you realize the pump error. Yes, you will face the hassle of emptying the deposit and a few euros for labor, but better to “leave it for another day” because the real damage happens later.

There is also an old saying that adding gasoline to a diesel vehicle “helps clean” the engine and the entire fuel injection system. That is false and nothing but wrong.

During the combustion process in a Diesel cycle engine, carbon deposits are generated resulting from incomplete combustion. These stick to the combustion chamber, valves, and injectors, and, like cholesterol, these dark deposits stick tightly to the car’s circulatory system.


Why is it said that it is convenient to add gasoline to a diesel engine?

Due to the very constitution of hydrocarbons, gasoline has a greater detonation power when ignited inside cylinders than diesel, generating vibrations that, technically, could eliminate the carbon above deposits.

To a certain extent, it can be said that this theory is true, but as long as we apply it to the case of an old diesel engine, one of those atmospheric ones that began to take their first steps in the 60s and 70s.

To a certain extent, it can be said that this theory is true, but as long as we apply it to the case of an old diesel engine, one of those atmospheric ones that began to take their first steps in the 60s and 70s.


These thrusters were designed in their day to be robust and reliable, and straightforward in their operation and maintenance. These units could practically run on almost any type of oil.


And considering that it used to be said that adding a small amount of gasoline to a diesel engine every 10 to 15,000 kilometers could help remove carbon, a low concentration of gas in the tank, it is true that they served as a therapeutic remedy. But with direct injection engines, it is another story.


If I put gasoline in a diesel engine, what happens?


As long as you don’t turn the ignition key, anything. But putting gasoline in diesel can cause damage to the fuel injection system and the engine. A diesel fuel pump operates with excellent tolerance to high pressures and is lubricated by a denser liquid. The lubricating properties are reduced by adding gasoline, which can damage the fuel pump through metal-to-metal contact and create particles that can cause significant damage to the rest of the fuel system.

This phenomenon occurs because, while diesel has a lubricant property in the pump, gasoline has the property of a solvent, increasing corrosion and deterioration in different components of the fuel system. Since modern diesel pumps (from the ’90s) are not designed to run on gasoline, parts such as gaskets and injectors can also be damaged. These repairs are often expensive, and the entire fuel line system may have to be replaced later.

Engine damage can also occur due to detonation caused by uncontrolled gasoline ignition since the compression ratio is much higher in diesel engines. However, if you catch the bug quickly, there is a chance you will get away with it. This is because up to 5% gasoline can be mixed with diesel without disastrous consequences (2.5 liters in a 50-liter tank). If there is no space to fill it with diesel in the required proportion of 95%, the tank will have to be emptied.


What if I put diesel in a gasoline engine?


Inadvertently putting diesel in a gasoline vehicle is more difficult to do. That’s because the former’s inlet nozzles are deliberately more significant than the latter, so the diesel hose does not fit into the inlet of a gasoline car’s tank.

However, the result of putting diesel in a gasoline car is not as catastrophic as the other way around. It will probably run harder, and the exhaust will be smoky, but it’s still much better to go no-drive.

Are there consequences to the mistake beyond the health of the engine?


The truth is that yes. Typically, damage caused by putting in the wrong fuel is not covered by the manufacturer’s warranty, and the insurance policy does not usually cover the error. However, some insurers offer a drainage service as a complement to the coverage you have contracted, so it is worth checking beforehand.

However, it is essential to note that driving a very short distance on the wrong fuel is not guaranteed to damage vital components in the ways described above.

Many specialists consider that many drivers have left the gas stations without realizing the failure and only ask for help when their engines rattle and start to scramble, stopping a few kilometers later, without long-term adverse effects.

Is there any other “cleaning” alternative for the diesel engine?

  • Additives It is the cheapest option (about 10 euros) and easy to acquire. Still, the reality is that some manufacturers advise against the use of this type of product due to the aggressiveness of the chemical substances they contain.
  • Sweep cleaning. In this case, the injection rail must be disconnected from the fuel inlet, and a “bridge” must be made for a cleaning liquid to enter through a pressure vessel. When the engine is started, the fluid circulates throughout the system, beginning with the injectors. However, like additives, there is a risk of damaging the injectors from the chemicals used.
  • Ultrasonic cleaning. This method involves disassembling the injectors and putting them on a test bench to check their sealing ability, spraying, flow rate, etc. Ultrasound cleaning is based on emitting a series of sound frequencies invisible to the human ear that make the part in question vibrate, removing dirt. Being the most recommended (and expensive) technique, the injector is thoroughly cleaned.

How can you avoid putting the wrong fuel?

The obvious answer here is that you have to be vigilant when it comes to refueling, but sometimes that is easier said than done. An alternative way to prevent this from happening is by placing a diesel fuel cap on the tank’s filler neck.

This cover prevents the fuel hose nozzles from fitting into the tanks for which they are not designed. There is also the possibility that many car rental companies choose, putting a sticker on the tank cap to clear up any doubts that may arise.

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