Sorry to say Swampu but the Ideal Gas Law does not apply in eeber's case, his is not a closed gaseous/liquid system due to a liquid leak somewhere that occurs below temperatures where a vapor phase can be established. Think steam engines for a better application.
Eeber (if not an air lock) if you have a TX heat exchanger this would be a good time to check and clean it too. Potential leak areas are:
- Head gasket or cracked head
- Exhaust manifold
- HX
- Turbo if JWAC
- Bad plumbing
Also, double check/test your oil for coolant. As suggested get a pro on these engines. Start with boatdiesel.