I Accidentally Put a Little DEF in My Diesel Tank: Solutions to Try

What should you do when you accidentally pour DEF in your diesel tank? You need to change your fuel filters immediately and highly recommended not to start the engine.

There are many web searches regarding “I accidentally put a little def in my diesel tank,” and if you also have this same problem, then check this entire article. Here, you will get a satisfying solution to this problem.

Accidents do happen, and when you accidentally put DEF in your diesel tank, then it can be a cause of worry for you. Don’t worry! Our researchers have done a lot of research and found the best possible solutions for this problem. Also, we will elaborately discuss how dangerous this issue can be in this article. Therefore, without wasting any more time, let’s get started.

Is It Dangerous If I Accidentally Put a Little DEF in My Diesel Tank?

Yes, it is dangerous if you accidentally/intentionally pour DEF in your diesel tank. If there is just a little bit of DEFin the diesel tank, then it is called DEF contamination.

The reason behind DEF contamination is that DEF is composed of water and urea, and it will contaminate your diesel tank’s fuel. DEF is made up of 67.5% water and 32.5% urea.

You see, it’s like when you mix water and oil, the oil will float to the top while the water or urea will sink to the bottom. Long-term effects will take place if the engine starts and is introduced to the DEF and diesel mixture.

In modern vehicles’ diesel emissions systems, DEF is utilized as an exhaust solution to lower nitrogen oxide levels in the exhaust. These systems are present on most modern semi-trucks, diesel pickups, farm equipment, and diesel cars. If you use DEF properly, it is a good thing, but if you use it improperly, it can cause severe issues.

When DEF is added to a diesel storage tank, it won’t just contaminate the diesel but also damage the fuel system if it is not removed instant.

In such cases, your vehicle will run badly or even might not be able to start. DEF is corrosive and damaging to many metals, including zinc, carbon steel, brass, magnesium, aluminum, copper, and nickel. After drying for a couple of hours, components contaminated with DEF will exhibit crystallization. As a result, the injectors and HP pump will be severely damaged.

This Video Might Help you Understand Practical Consequences!

What Happens If You Put 1 Gallon of DEF in Diesel Tank?

It mainly depends on the capacity of your diesel tank. The higher your diesel tank’s capacity is, the lesser it will cause problems. A small amount of DEF in your diesel tank won’t cause much harm. For example, if the capacity of your diesel tank is 300 gallons, then there is not much you should worry about.

However, if your diesel tank’s capacity is 3 gallons, then there are serious consequences. It will most probably result in a disastrous fuel system failure. The fuel system’s seals will all be eaten away by the DEF fluid, and the injectors will become clogged.

If you do not make any attempt to start your vehicle’s engine, then you need to immediately drain and flush your diesel tank, which would likely prevent any further damage. Otherwise, it will severely damage your fuel filters and, in the worst case, can even damage your engine. You can check the below video to know more about what happens when you put 1 gallon of DEF in your diesel tank:

What to Do If You Put DEF in the Fuel Tank?

It is recommended that you change your fuel filters and drain that out immediately after you put DEF in the fuel tank. Don’t start your vehicle’s engine. You are required to drain the fuel tank and the fuel water separator. Also, you can replace your fuel system, but it is much too costly. In addition, you can take your vehicle to your nearest repair shop and inspect it by a certified mechanic.

Remember, there might be some part that needs repairs or replacements due to the DEF fluid having been there, particularly if you started your vehicle’s engine. An expert user said regarding this on Reddit,

The following steps are recommended if DEF accidentally pumped into a truck’s diesel tank. If DEF in accidentally added to a diesel storage tank follow steps #2, 4, and 5. Do not start the engine and contact your engine service providerDrain the diesel tank and dispose the fuel following your local regulationsDrain the diesel fuel conditioning moduleFlush the fuel systemReplace all filters.”  

To learn more about what you should do if you put DEF in your vehicle’s fuel tank, you can check the below video:

Frequently Asked Questions (FAQs)

Will DEF hurt a diesel engine?

Yes, the DEF fluid damages a diesel engine, and the damage can be severe. The damage to the engine mainly occurs because of the corrosiveness of the DEF. When the DEF fluid enters your vehicle’s fuel system and spreads all over the engine, it will ultimately damage the diesel engine. The fuel system lines aren’t compatible with the DEF fluid and will slowly corrode over time.

What happens if you mix DEF with diesel?

When you mix DEF with diesel, then something bad will happen to the engine’s fuel system. The full form of DEF is diesel exhaust fluid. The DEF fluid is 2/3 water and 1/3 urea. Like water, when you mix DEF with diesel, it would probably sink to the bottommost of the diesel tank and be taken in by your vehicle’s fuel system.

How do you get DEF out of diesel?

To get DEF out of your diesel tank, firstly, make sure that you do not start your vehicle’s engine. Then you need to drain and flush your entire fuel system. After that, replace your fuel filters immediately. In some cases, you may need a full fuel system replacement.

Does DEF float in a diesel?

No, DEF does not float in diesel. Oil is less dense compared to water, and diesel is a type of light oil. On the other hand, 67.5% of the DEF fluid is water. So, DEF is denser than diesel. As a result, the DEF fluid will settle down to the bottom of your vehicle’s diesel tank. Keep in mind that oil does not mix with water, so the diesel will not mix with the DEF either.

Does insurance cover DEF in fuel tank?

Sometimes insurance companies cover the DEF damages in the fuel tank, and sometimes they do not. For the first time, your insurance company may cover the damage, but from the next time, it won’t. Keep in mind that not every insurance company will provide coverage for damages caused by DEF. Also, some insurance companies have a sub-limit that might not cover the total cost of repairs.

What happens if I put a small amount of AdBlue in my diesel tank?

If you add AdBlue to your diesel tank, then it can cause you thousands of dollars worth of damage. If you put AdBlue in your diesel tank and start your vehicle, then it will cause very severe damage to your truck’s or car’s SCR system. AdBlue isn’t a fuel additive or fuel. It is a mix of ionized water and manufactured urea. AdBlue will damage plastics and corrode metals used in the engine and fuel system.


You can get confused sometimes and accidentally pour diesel exhaust fluid into your diesel tank instead of diesel oil. However, this accident can result in severe consequences for you. A DEF in your diesel tank can completely damage your fuel system and even cause damage to the engine. Lots of people want to know the solutions to the “I accidentally put a little def in my diesel tank” problem.

If you are also facing this problem, then you need to know why this happens and also the solutions to it. We are hopeful that this article has helped you to know these things and now you can easily solve this problem. Still, if the problem has not been solved or if you have any more queries, then do let us know in the comment section. 

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