I was going to suggest you might have a piston or two not doing their fair share because they are stiff and seizing in the caliper due to ingress of grot.
Why add a “bleed screw” to the top of the head? There has to be a better explanation than bleed screw. There’s already one on the pump at the bottom of the system.
The pump one is a drain screw, the head one you undo when filling the coolant after a drain to dispel the air.
Generator/radiator fan
in Beta
Posted
Sounds to me like a defective regulator, do make sure it has a decent ground though.