# Car was rear-ended, DEF leaking?



## sbalea (Mar 12, 2014)

Hi all,

Unfortunately our 328d got rear ended today. Second time it happened in one year since we got it.

On the bright side, the damage is minor, nothing structural appears to have been impacted. On the not so bright side, one thin hose appears to have detached and is slowly dripping a clear fluid, which I assume is DEF. With engine running the flow of fluid is more consistent. The fluid appears to have a very faint smell - I am not sure how DEF is supposed to smell like, so I cannot tell. The car drives normally, and I did not get any warnings at all so far.

Not sure what to do in this situation. It will probably be a few days till the insurance works the claim out and authorizes repairs. If the DEF runs out in the meanwhile, I suspect I won't be able to start the car. On the other hand, I'd rather not try to patch it myself, don't want to give them reasons to mess my claim.

Attaching pics of the rear end underside. Any advice would be very much appreciated.

Thanks


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## GreekboyD (Jan 25, 2012)

The DEF will crystallize and look chalky when it dries it up. If it is the DEF, you will most likely see a message to refill it very soon.


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## sbalea (Mar 12, 2014)

Judging by the chalky brownish spot left on my driveway, definitely DEF.


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## Hoooper (Jun 17, 2013)

All those white specks on the bumper are DEF. I wouldnt be concerned about driving it. Even if the computer senses that the system has failed you still get adequate warning (is it 250 miles? its different from the low DEF warning). If such a situation comes up just drive it to the dealer and get a loaner, the insurance should cover that due to accident related repairs.


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## AutoUnion (Apr 11, 2005)

Yup, that's a DEF tank leak. The crusty white stuff on the bumper is the key here


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## glangford (Dec 11, 2013)

DEF can be corrosive, being a pretty strong base. I'd rinse everything off and try to pinch the hose off so it doesn't continue to run out when driving.


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## Doug Huffman (Apr 25, 2015)

glangford said:


> DEF can be corrosive, being a pretty strong base. I'd rinse everything off and try to pinch the hose off so it doesn't continue to run out when driving.


I do not believe that is so, that DEF urea aqueous solution is a strong base. Urea pKb basicity is 0.18. Indeed, there is the statement "Dissolved in water, it is neither acidic nor alkaline." (https://en.wikipedia.org/wiki/Urea)

It is an electrolyte and does form corrosion cells in susceptible metals.


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## sbalea (Mar 12, 2014)

Got the car in the shop before DEF ran out. Not my problem now


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## glangford (Dec 11, 2013)

Doug Huffman said:


> I do not believe that is so, that DEF urea aqueous solution is a strong base. Urea pKb basicity is 0.18. Indeed, there is the statement "Dissolved in water, it is neither acidic nor alkaline." (https://en.wikipedia.org/wiki/Urea)
> 
> It is an electrolyte and does form corrosion cells in susceptible metals.


The same source says



> Ammonium carbamate solutions are notoriously corrosive towards metallic materials of construction, even the more resistant forms of stainless steel, especially in the hottest parts of the plant such as the stripper


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## Doug Huffman (Apr 25, 2015)

*Your assertion was "DEF ... a strong base." It is not.* It is an electrolyte allowing current flow between corrosion cells.


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