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

[Chamberpains]

You won't be just pressurizing the coolant to see if it will hold pressure. Your going to need to drain the oil, remove the oil pan, then pressurize the coolant system up to 20 PSI. Let it sit over night and check up around each cylinder to find coolant running down. Then you will also want to bar the engine over to see if any of the cylinders start leaking or gurgling coolant.