2011 Cascadia dd15. Lose 1-2 gallion cooliant a day. Any ideas ?

Gotta be a leak somewhere.

Get the engine thoroughly washed, run it, then shut down and get down there with a good flashlight and look for ANY trace of coolant. Especially check the hoses by the clamps. Freightliner really likes the cheap compression clamps. You should go through and replace those with the more standard screw type hose clamp.

Also check the lines leading to the cab heater core and the bunk heating system. There is generally a separate heater core back there somewhere to provide heat off the engine during idle, regardless of the presence of aftermarket bunk heater (idle reduction tech like a Webasto or Espar).

 

Potassium and sodium are coolant additives. You are getting coolant in the crankcase. EGR cooler would be a good starting place to check.

 

EGR cooler is most likely to be the culprit. Pull crossover pipe and check for signs of coolant passing thru.

 

A bad EGR cooler wouldn't leak into the crankcase though. It would leak into the intake.

 

Here's a video on how to do it.
Freightliner Cascadia DD13 DD15 DD16 engine egr cooler replacement

 

And here is a video on how to diagnose missing coolant.

Freightliner Cascadia DD13 DD15 DD16 engine burning coolant missing coolant

 

You are correct, an EGR cooler leaking introduces coolant into combustion chamber via intake. The sodium and potassium used as part of coolant package does not react during combustion and is carried from cylinder liner via the oil film to the crankcase and is suspended in the motor oil.