It's been 6 months since I replaced all this parts and the coolant. Does the air stay that long traped in the radiator? How can I remove the air from the system?

After filling the system, I did remove something like a drain plug on the thermostat housing thinking that that was the way to remove air from the system. During the first week I did have to add some coolant because of air getting out of the system. Now I don't know how to remove more air. Should I remove the upper hose from the radiator neck to let the air get out or something like that?

Yesterday I also noticed that there is a small leak starting somewhere near the upper neck of the radiatior. Is it possible that the inflated hose is the source of the leak or it is a sign of a radiator failure?

Thanks for you help guys.

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Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter