The Coolant Air Bleed Stuck!

As a follow up to my over heating condition, I've replaced the thermostat and the water pump to no avail. The mechanic by default also had to perform a flush. The car is still prone to over heating. I'll admit not as bad as before but the possibility of that happening in slow moving traffic is still there. I noticed however that the coolant air bleed was not touched at all. I know this because prior to taking the car to the mechanic, I tried to bleed the air thingy myself to no avail. It was stuck! I know the righty tighty / lefty loosy saying. So before breaking the stupid thing myself, I figured let the mechanic break it :D . Unfortunately, he was smart enough to realize the thing was stuck and left it alone...

My question is - any suggestions on how to loosen the darned thing?

BTW - the two top hoses on the radiator are piping hot, the bottom ones are not too hot. To the naked eye it appears that the radiator is not filled to capacity. I squeeze the hoses and coolant returns to the reservoir.

Try spraying it with PB Blaster when hot and check it in the morning. It should if low on coolant normalize and you can refill the bottle when cool in the morning.
I think your ready for a clean and rod or new radiator.