Concerning trapped air, the B-series Cummins and most other diesels actually have a plug in the block at the highest point; you remove that plug to allow the air to escape; you can then bleed off any small amounts of air by loosening the plug.
Some of us replace that plug with a pet-**** valve that simplifies the process.
I do not know whether such a plug exists on the IDI engines, but I would almost bet that there is one.
If no such plug is available, you can accomplish the same thing at the temperature sending unit, providing it is high enough.
One might could even install the sending unit in one leg of a TEE and a drain-**** in the other leg.