IDK if it will be helpful, but here's a brief explanation of how the system is supposed to work.
Normally, the radiator and rest of the cooling system is totally full of coolant, primarily a mixture of water and ethylene (or propylene) glycol. As the engine heats up, the coolant expands and starts to pressurize the system. There is a calibrated relief valve in the radiator cap that lets the excess expanded coolant out into the coolant tank. The radiator remains full without any air. If there was a small amount of air in the radiator, it gets pushed out into the coolant tank as the coolant expands. When the engine is shut off and cools completely, the coolant contracts and more coolant is drawn from the tank to take up the space so that there is no air in the radiator. When the engine is totally cool and you take off the radiator cap, you should see it completely full to the brim. This is described on page 441 and 442 of the manual.
Do not ever attempt to remove the radiator cap unless the engine is completely cool.
The tank is there only to allow a place for the expanded coolant to go, and then to provide some when the engine cools. It's not air tight and doesn't participate in cooling of the engine. In fact, you can see a gaping hole in the front of it below the fill cap in the photo on post #5. The level in it is not important other than there being enough to supply the small amount needed when the engine cools. My tank also shows some blue residue from evaporated coolant. I suspect this is from some that splashes out of that hole when hitting bumps.
Back in the day, cars were designed to have an air space in the radiator to allow for expansion. If there was too much coolant in the radiator, it'd get pushed out the overflow onto the pavement when the engine heated up, and as the engine cooled, air would be drawn back in. This automatically ensured there was enough air in the radiator.