No idea on hours, drained coolant to pull intercooler for changing exhaust gaskets. Coolant looks terrible, green. I have suggested replacing with either DCA based, or ELC to keep things in shape. Owner is concerned changing coolants will promote seal failure. I guess I've heard it before, water pump mainly, but what is the right answer?
Deere's Cool-Gard II would be fine in that engine. But if the owner is that worried, then continue using a DCA based coolant.