96 integra LS

radiator cap holds pressure
radiator no leaks
coolant in coolant reservoir seems higher than normal
visually see a small pulse in the coolant reservoir
a lot pressure build up after removed the radiator cap overnight
i had to pour some coolant to the radiator from the reservoir
upper radiator hose very stiff when running
no signs of and substance in spark plugs
no signs of substance coming out of tailpipe aka white smoke
no signs of milky substance in oil in dipstick
no signs of milky substance in the oil cap
idles at 1.5k
car overheats in idle
car in normal temp. while driving
fan works fine

what does it sound like?

 

Have you tried bleeding the system?