Peterbilt DEF fluid Question.

Hello, New to forum.

My question is. I have a 2013 peterbilt 348 paccar 8x, its a water truck. The Fabrication shop has a bus heater running off coolant that circulates with the DEF warming system. Its currently not circulating any warm coolant to my heater.
my theory is that the DEF system doesn't get heated until its below a certain temperature?

Am I correct or should I get the truck in the shop? It also isn't heating my DEF fluid tank.

 

Would you know what temperature that solenoid opens? Does it go by truck thermostat temp or DEF fluid temp? Its been -12 outside and still not circulating the coolant. The truck is kept inside during the night so I assume the DEF fluid would not get cool enough for the solenoid to open.

 

Thats what I figured, what a pain. Thanks

 

I like to my own work on the truck. What would you think of Y'ing off the coolant inlet to my cab heater then Y'ing back into the Outlet from the same spot? Would there be enough flow/pressure to complete the circuit

Thanks!