Does DEF Crystalize?

pegmikef

Well-known member
My son called today and said the DEF in his driver/trainer's 18 wheeler caused some kind of crystalization and the rig would not go over 5 MPH. Did I misunderstand him or does such a thing happen? The rig is a 2011 with 310k miles, but I don't know what make. DEF is what got my attention.
 

danemayer

Moderator
Staff member
On my GMC, if the low DEF warning is ignored, the engine will be throttled back, eventually to 4mph.


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pegmikef

Well-known member
On my GMC, if the low DEF warning is ignored, the engine will be throttled back, eventually to 4mph.

Yeah, My Ford does the same thing if it is low, but this is a professional long haul driver and I don't think it was low . . . he said something crystalized. I just had never heard of anything like that on any of the forums . .
 

murry135

New York Chapter Leaders - retired
I have seen it crystalizw when it is spilled on the ground and side of my Ford. I guess it can crystalize inside the tank if it his verylow or empty on the the tank walls.
 

porthole

Retired
I have seen it crystalizw when it is spilled on the ground and side of my Ford. I guess it can crystalize inside the tank if it his verylow or empty on the the tank walls.

Ditto, get a little sloppy and you will see it a short while later.
 

brianharrison

Well-known member
Common knowledge that DEF is a water based solution of UREA (1/3 Urea, 2/3 water) specially formulated for OEM vehicles. Urea is an organic salt. At certain low temperatures (~12F), the UREA can "salt out" in solution - ie appear to crystalize. As the temp is raised, the salt crystals should re-dissolve and go back into solution.

As well, if the concentration of UREA increases - ie you spill it and the water evaporates - you will also see the crystals form at ambient temp. I guess it could do this in the tank if the conditions were right.....

If the DEF injection went cold, plugged up with crystals and stopped injection, the engine computer would power down - my thoughts.....

Hope this helps.
Brian

EDIT -> Link to online information of DEF solution properties and behavoirs....
 
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mmomega

AnyTimer
It will indeed crystalize if it has a chance to dry completely. I have spilled a tablespoon or two before right at the filler neck and after it completely dried up it looked just like salt, also if you have a black truck like I do and spill any down the side it will dry almost completely white so you can see it easily. Now don't worry it will wipe right off and I haven't noticed any damage to the clear coat by letting it dry and wiping away.
 

lwmcguir

Well-known member
My son called today and said the DEF in his driver/trainer's 18 wheeler caused some kind of crystalization and the rig would not go over 5 MPH. Did I misunderstand him or does such a thing happen? The rig is a 2011 with 310k miles, but I don't know what make. DEF is what got my attention.

Since the DEF is nothing but diluted UREA with pure water this isnt going to happen in the tank. Somthing else has to happen. As the other posters noted any time you let anything that contains ionized elements dry out it will form crystals. Hard water will do the same. Nothing to worry about in your truck at all. This has to be either contamination of the DEF or equipment failure. Try it by pouring some DEF in a beaker and watch it. It wont crystalize until it evaporates to the point it is no longer soluble.
 

mdamerell

Member
DEF must be keep heated to prevent freezing. If the DEF tank heater fails the doser valve will clog, engine will de-rate and then shutdown.
 
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