loss of coolant

I doubt it. My guess is it leaked out or it was drained out at some point. It can permeate through silicone hoses but I'm not seeing the system becoming nearly completely empty due to that, maybe a gallon or 2 at most.

 

It may have a leak, or it could have been drained before it was parked in prepreation for some work. Coolant doesnt evaporate much/at all AFAIK in a closed system. Best best is to fire it up and go over anyplace that coolant passes through with a bottle of soapy water looking for leaks.

 

Did you get the oil and water temps up to operating temps at least 190? The motor at 960,000 miles already had an overhaul once and is probably near the end of second overhaul. Its a c13 acert. Check for white smoke out stacks.
You said it was the ex husbands truck from 6 years ago. Maybe the ex sabotaged it becuase he didnt want the wife having it

 

good to go then. run her till she blows

 

I have a C13 kcb .1545000 miles no rebuild still running

 

I have this Truck from 10/2009 have repairhistory