It's the crank sensor!
Join Date: Nov 2007
Location: Central Minnesota
If you're losing coolant and you have verified positively that you have no leak (have you?) then the head is a primary suspect. With loss of coolant, you're either leaking it or burning it.
Unfortunately, the compression test is not the best test for troubleshooting a cracked 0331 cylinder head. I've personally seen this test pass with flying colors with a cracked head. And not oil has the "milkshake" appearance either; some do and some don't. Much of the coolant actually is burned off.
Here is something easy that you can start with. Remove the oil fill cap and with a good light, inspect inside near cylinders 3-4. Oftentimes (not always) you can see the coolant seeping through the crack with a pressurized cooling system. Pressurized means either a hot engine turned off or pressurize the system using a cooling system pressure tester (can be rented) which hooks up to your radiator cap and pumps up to pressurize.
Good luck and keep us updated.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!