Overheating

Check radiator for cold spots with fan disconnected and engine hot and off. If you feel any cold spots radiator is no good and needs replaced. Otherwise have coolant system pressure checked for internal leaks.

This apparently was caused by the loose radiator cap, and that is not going to damage the thermostat. You are right about the air pocket. I do not know why you did not list the engine size when you have an engine-related problem, but the V-8 engines usually self-bleed by themselves. If it is necessary to bleed the cooling system, there will usually be a bleeder screw on the thermostat housing. When there is not, look for a threaded plug or a temperature sensor on or near that housing that can be removed. If you need to remove a sensor, unplug it and do that while the ignition switch is off to avoid setting a diagnostic fault code that could confuse someone in the near future. Most fault codes self-erase after fifty engine starts, but it is easier to just avoid setting them in the first place.

Please let us know happens so it will help others.

Best, Ken