SCR DEF Freezing Question

Been having a bad winter this year with my 2013 Western Star 4900SB/DD15 Detroit. We have had a few weeks of minus 30*C and sometimes even colder and I've had quite a few instances of the truck going into derate as soon as I leave the yard which requires a trip to the dealer to have the code turned off. It is because the DEF system has not thawed out. All the factory heating components are working, no other faults.
So I even tried starting the truck and letting it run for a couple hours before I leave and it has still froze up on me. (which all the excessive idling can't be doing the DPF any good.)

So I have a question if anyone has any idea? Is the coolant flow an open loop through these DEF tanks or is there something that shuts off the flow? I'm wondering if I put a Webasto (or Espar) on this thing like I had on the old truck, if it will circulate the warm coolant through the DEF system when it is parked at night?
I was told the ECM shuts off coolant flow when it thinks it is warm enough, but not sure what state it is in when parked cold.

Any other ideas? It has also happened with our 2012 Coronado 122SD/ISX, but not as frequently as the Star.

Thanks for any ideas.

 

Thanks a lot everyone!! Very helpful information. I appreciate it.

 

Talked to my dealer about trying to heat the system using a Webasto, but I never got anywhere trying to figure out plumbing.
But I did learn I was doing two things wrong. I was running a winter front which they say can cause problems.
Even Cummins has recently stated not to run a winter front. Only problem is without it my air freezes daily despite draining all my tanks a couple times a day.

Other thing I was doing wrong was draining my air tanks before shutdown so that I had more air to blow the condensation out. Then I would shut down and drain the tanks. Therefore it didn't have enough air to blow the def fluid back.

So we'll see what happens this winter.

 

New air dryer and power at the heat element? It freezes right after the compressor all the time under the cab.
You can't even get at the compressor, it's on the back of the engine.