What happens if you put Diesel Exhaust Fluid in your diesel tank?


DEF equipment Houston TexasWhat happens if I pour Diesel Exhaust Fluid inside my diesel tank? This is by far the no.1 question online; throughout all multi media channels.

We have been researching this question for sometime but need your help in filling in the blanks, the point of this entry is to help those of you searching for answers like this.  

So, first of all; Diesel Exhaust Fluid has the traditional blue cap on the tank.  Diesel also has a colored coded cap and it is typically green.  With that being said, we are unclear as to where the problem may be happening; at the retail pumps or private locations?  If you have some input, let us know here so that we can update this entry.

Ok, let’s jump in. Keep this in mind, the dispensing nozzle for Diesel Exhaust Fluid is smaller than the diesel dispensing nozzle.  So, what may be happening is that the DEF dispensing nozzle is finding its way into the diesel tank.  Of course, you cannot take the diesel nozzle and put it inside the DEF tank because of the larger diameter.  Keep this in mind. 

We found ourselves in different forums adding to this ongoing conversation and here is what we have found thus far.   The main problem lies with the corrosiveness of DEF.  So if we assume that there is a misfill of DEF into the diesel fuel tank, the problems that you will encounter may occur as DEF (although classifed as a non hazardous chemical) is corrosive to some metals. This of course leads will have a negative effect inside the compelte fuel system.  Again, keep in mind that the material’s used inside the fuel lines may not be compatible with Diesel Exhaust Fluid.


DEF houston texasWe are aware of engine failure reports, but again no hard informatio on the step by step pricess to what to do next.   The next logical place to look for data is into the AdBlue market in Europe; hoping to have a little more history and comments in those forums.  We also continue to look for OEM data to be availabe, if you know more information please post here. 

The very nature of this technology being new to the USA is what is sending people searching for answers.  So again, the biggest concern seems to be corrosiveness inside the fuel supply/engine. We do not claim to have clear answers but we will take a stab at trying to guide those that have unfortunately been hit with this dilema.

We all know that Diesel Exhaust Fluid is 67.5% water, and 32.5% Urea. Since water is the bulk of the composition on DEF; the areas of concern may be the following: (aside from the corrosivenes we have already highlighted).



1. Injectors may need to be removed / cleaned propertly.

2. All fuel lines, fuel pump, must be propertly flushed and cleaned.

3. Fuel filters must be serviced.

4. Remove the water fuel separator and install new one.

5. Remove and flush all existing fuel from the tank and inspect the tank.

6. Inspect fuel line assembly, fuel vent fittings; and hoses.

7. Address probem right away.  DEF sitting in the engine will cause much more damage due to the corrosiveneness of Diesel Exhaust Fluid (DEF).

Common sense tells me not to start the engine, and drain the tank immediately to avoid any further contamination. 


Transliquid technologiesOk ladies and gents, chime in and let’s build a good white paper to help our young industry.



  • Robert Rivas Publicado 2017-01-20 22:09

    Put def in diesal tank. Started it. It stopped running. Next day emptied the tank. Blew out the lines. Put additive. Started up. Is running fine. Is that the extent of it.?

    • MelissaR Publicado 2017-01-23 15:26

      Robert, it is suggested that you contact your closest dealership for further instructions.

  • Lynn Publicado 2017-04-19 20:40

    I put maybe 1/2 gal in my tank my pickup was running so I to it to the shop and he told me to put Lucas in I did I got worried and took it back and told him to drain it and flush and change fuel filter . Anything else

    • MelissaR Publicado 2017-04-21 10:16

      Lynn, you did good by flushing and changing the filter. Hopefully the amount you put in was not enough to do any damage. Only time will tell. Please let us know if anything else happens.

  • Karen Walker Publicado 2017-05-12 23:25

    Hi My Dodge dealer put 2.5 gallons of Def in my diesel tank at the dealer, the detail boy did it, now I did not know he put it in the wrong tank and started it up and drove 20 ft before warning lights came on, and truck started shuttering and shaking and would not let me turn it off and then died. The dealer knows they mess up but so far all they did was drain the tank, clean out and and changed fuel filter twice .This is a brand new 70k truck and it appears that there is not enough information or history to say for sure that there will not be further damage to components in my my engine. I have consulted and attorney but can you give me any advise as to long term issues?

    • MelissaR Publicado 2017-05-15 15:27

      Unfortunately we cannot know the extent of the damage to your vehicle, or what long term issues you may encounter. My only recommendation is to request the dealership to replace all parts that may have been damaged, which are all fuel related components. Good luck!

    • manny Publicado 2017-10-11 21:40

      well I have looked at several of these and if the dealership is charging insurance companies or vehicle owners they replace everything so why should it be different when they have to pay the real issue here is bottom line the dealerships are there to make money I have a 2016 dodge long horn at a dealership right now and they gave me a 24,000 dollar bill for the same thing I would make the dealer replace all parts effected from the fuel tank to the fuel injectors and everything inbetween

  • Andy Publicado 2017-08-08 05:00

    Went and got fuel at a truck stop, and on a dodge, the def filler hole and diesel are right next to each other. As I attempted to pull the def hose out to insert into the correct hole, there was still a little in the hose from previous user, and had gone into diesel hole by accident ..maybe as much as 6 ounces..what quantity will actually hurt the motor?

    • Jeff Publicado 2017-08-10 05:39

      Andy, you can buy a magnetic green diesel cap for the fuel tank on the internet for around $6-20. Best investment for a 70k truck

  • Al Publicado 2017-11-03 11:53

    I put 2 gallons of def in my diesel tank it ran for 5 min and quit the dealer wants $8300. To clean the dystem you have any suggestions it is s 2017 F250.

    • Dumb old man Publicado 2018-10-19 11:28

      Did same dumb think somehow. . Tow truck got me home. I drained tank using return to tank and electric fuel pump. Flushed with new fuel, added some Lucas diesel treatment for the hell of it. Started truck after changing filters. Changed filters x2. Put in new fuel…. cost 15 gallons diesel wasted, 8 bucks and 45 dollars on 2 sets of filters…an ALL DAY project.. Truck runs.

  • Frank torre Publicado 2017-11-20 20:33

    I just did the mistake to put around 6 oz more or less in my diesel truck the Tank was 3/4 full run for 150 miles and the truck star running ruff for about 2 min and them all was good I call a diesel mechanic friend and he took me to bring the truck to his shop in a flat bed bc I had a court left of diesel and he want it to drain tank flush lines and change filters and drain the water separator do you think the truck should be k I it was a small amount to almost a full tank any reply will be appreciated

  • Master Publicado 2017-11-20 20:44

    You need a new motor now sir

  • Kevin Hatfield Publicado 2017-12-05 06:49

    This past weekend I stopped at a truck stop to fuel up my 2006 GMC 2500 6.6lbz. I was pulling my camper so I pulled round back with Big trucks. I topped off fuel and drove home. When I filled up I put 18 gallons in. Got up next day and truck would crank and run for 30 seconds and shut off! Does that sound like exhaust fuel in fuel tank? Any help would be appreciated! Thanks

  • Art Publicado 2017-12-21 21:45

    I was puttin deff into 2500 ram 2016. Spout came off deff and it got into fuel tank. Did not think anything about it. Drive 1/2 Mike and truck shut off had to b towed to dealer they told me all fuel parts have to b replaced $22,000 plus tax. He said he gets 3 of these deff problems a month. Ram needs to fix this problem if deff and fuel lines being so close together. As Rsm owners Ed should fight Ram and make them pay. I m out the money

  • David Collins Publicado 2018-02-10 14:25

    Does add blue affect oil my Triton has sieved motor the oil is like tar there saying I put add blue in my deisel tank

  • Mark Publicado 2018-03-23 21:51

    One of our crew put several gallons of Def in the diesel tank of an 05 Duramax. I called my mechanic who said add an additive it would be fine. Not true. A few weeks later the truck was acting funny so we took it back to the same mechanic. He said it had a blown head gasket, replaced all head gaskets, no change. Ended up having to change the whole motor, fuel lines, everything. Big expense, do not put def in the fuel tank and if you do don’t drive the truck until you get it cleaned out.

  • Chip Publicado 2018-08-12 12:08

    What is the best to flush you fuel system and lines?

  • Richard Publicado 2018-09-15 10:16

    Just made the mistake. 2017 Nissan Titan XD. 2 gallons of DEF in fuel tank. Drove about three miles, truck started shuttering and now not crank. About to take to dealer. If I don’t tell them that there is DEF in tank (indicator light showing water in fuel tank)… will they know it’s DEF?

  • Jeanette Publicado 2018-11-20 12:47

    Dodge did not put fuel caps on the truck and unfortunately some def was put into the desiel accidentally. It was run maybe 10-12 miles. Showed up as water in gas on the dash. Took it to the dealer another 3 miles. Everything was cleaned out – fuel lines, gas filter changed, tank was drained. We are waiting to see long term effects. We ordered magnetic gas tank lids to prevent future errors. But am wondering about effects on fuel mileage. This is our first time pulling the 5 th wheels since “the incident”. Fuel mileage before was 12 mpg and now it is 9 mpg. Thoughts?

  • Broke$RN Publicado 2019-05-17 23:49

    Just got my Titan XD truck back after something like that apparently happened. $34,000! Bought a locking diesel cap. I’m thankful I paid for great insurance coverage.

  • Joshua Publicado 2019-06-29 08:21

    I put about a cup of def in a full tank of my 2019 f250. Not thinking about it was running nothing happened then I woke up and started it it ran and died then started up again. Water in fuel light came on getting fuel treatment and filter change. Seems like it ran fine right after it started back up?

  • James stroud Publicado 2020-06-14 15:27

    I put 18 gallons of def in my f350 truck by mistake, the truck would not start, going to drain fuel tank and new filter, hop I don’t need an engine should I take the injector lines off?

    • noxguard Publicado 2020-06-17 09:20

      We recommend you get a specialist to check your unit and do not try to start your truck to prevent further damage.

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