2013 ISX 15 rapid sudden coolant consumption

[Nerv]

Last week had truck doing a regular run it does, super light load 20,000lbs, next day when truck was turned on in the morning there was a small cloud of white smoke come out and continued out the day, no codes or any other troubles, about 10 hours later got a low coolant light, checked the coolant and it was low, opened the cap and it shot back up to normal level, oil was good and clean normal level. Made it about another 350km until the coolant light came back on, noticed it was about 3 litres low and coming out the overflow, shut truck off filled it and truck wouldnt start. Right away I thought it was something serious, called a tow truck and towed it into town as we were in the middle of the mountains.

Had someone come out and bar the engine over, was freely spinning, cleaned up battery terminals of slight corrosion and truck fired right up. Kept firing up and no other running issues. Truck sat for a week and was still a 30 min drive and 2 hour ferry back home. Had to fill 3 jugs of coolant after the tow, which was very odd, I right away assumed the EGR cooler, drove it to ferry, no lights came on. Had to shut it off , 2 hours later wont start again ON the ferry. Now Im panicking as the ferry is going to sail back if i cant get the truck started. Engine still freely spinning, still thinking battery is bad as well, put it on a charger and it fired up, drove it 1km to closest shop, shut it off.

Heres where the story takes a bad turn and whether im to blame or not I just couldnt leave it where I didnt trust anyone to touch it, either way now the engine wont turn over, right at this time now the oil is overfilled and brown… and Im beating myself up for not leaving it where it was, or finding someone in that area to work on it..

Background on the truck, demaned. File was fixed on here, wasnt horrible but still needed work, truck had a slight rough idle at times but if engine was idled up like I always do then it was smooth out. Engine was rebuilt under warranty at 350,000KM, currently milage is 995,000miles. Yes, I know it is in its old age, and I was already doing research on in-framing it in the next couple of months. In the last 3 years, NO coolant consumption not even 1 litre, oil changed every 10k miles, even at this interval the oil still had a slight golden hue to it. Average engine load throughout lifetime was exactly 20%. Driver abuse history shows no difference from before, no over speed events, coolant temps were same as before this happened, so my question is how does this happened quite rapidly and suddenly without an overheating over spooling event? Just old age im guessing? Please let me know best options at this point and what to do, this truck is obviously used to feed my family, and I need to make sure its fixed properly. I never neglect it and try to my best to avoid mistakes, and im really beating myself up for driving it, note to others if any kind of coolant consumption, we always want to not think of the worst case scenario, and that was me.