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

[Waterloo]

Check the EGR cooler first, pressurize the coolant system and pull the hose off the back side of the EGR cooler, put a saucer or something similar to catch any leaking coolant while the truck sits overnight under pressure, 20 psi. If it is bad, you will find coolant, and at least have a place to start.

Look for leaks in general too. It will be a good idea to drop the DPF/DOC cans too to inspect, they are more than likely toast if coolant is coming out the exhaust, no matter its origin.

I would start at the EGR cooler and then go from there. No bubbles or pressure build up in the coolant tank is a good sign.

I would also head up to NAPA, if they are open in your area, and get one of their "Block Test Kits", they run around $50, I have used them in the past and they work. Just make sure you have the motor nice and hot before running the test.