Cummins ISX 7CEX emits white smoke, smelling coolant, then another day not?

[ichudov]

I bought this truck at auction. It has Cummins ISX 385 engine "7CEX".

I brought it home and did not notice anything, unloaded from my lowboy and took it for a quick ride. After a few minutes I noticed that it emits a lot of white smoke. The smoke seemed to smell of coolant. I also notice that though the smoke was copious, it disappeared momentarily when I would push the gas pedal to rev up the engine. Video:

https://youtu.be/5vtMqeNajNg

A day later, I went to work to look at it closely, added more coolant and started again. To my surprise, the exhaust on the second day did NOT smell of coolant, at least when the engine was cold. Here's the second day video:

https://youtu.be/_roBlfNtnIc

I shut it off without much investigation but I would like to properly examine it and understand why it may be smoking and giving these symptoms.

I would GREATLY appreciate your suggestions.