... I still can't figure out how you would get trapped air out of the radiator without a radiator cap. Sucking up the hoses ain't going to do it. The air needs to be forced out by high fluid flow or something if you can't relieve it directly...
Air is a fluid, albeit a compressible fluid, the same as the coolant. If you evacuate the air from the system, there is none left in the radiator. The fact that the radiator, solid tubing, coolant pump, etc. don't collapse, does not mean that air is still in them; their walls are just strong enough to withstand the pressure differential from the external atmospheric pressure.
When you open the system to the refilling coolant, it will fill all of the places where nothing is present, provided that the acceleration due to gravity of the coolant mass is overcome. Otherwise a void may be present of vacuum. A vacuum volume does not act like a restriction as a volume of compressible air at atmospheric pressure would. And, as the coolant system builds its own pressure (due to thermal expansion) the vacuum volume decreases.
