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

[JimT]

Oh, one other thing. At one point I too smelled coolant during engine operation and was losing a small, but noticeable amount. It turned out that my pressure cap was bad and allowing coolant to come out the overflow tube. A new cap immediately resolved that problem.

The smell was deceiving since the engine fan would blow the air over all areas and make the source harder to determine. It's possible you have different problems each with different symptoms.