if its thermostat and its stuck open it will take a long time for the gauge to move up, if it moves up much at all and get any heat.. if its stuck closed u will overheat.. of the 2 stuck open is better at least the antifreeze is moving some..your thermostat may just be intermittently sticking they can do that.. if your antifreeze isnt moving but its in the radiator maybe stuck closed it will over heat its not moving out of the radiator.. water pumps make noise, bearing whine noise, weep antifreeze out of the weep hole. i think they are pretty consistent when they go, not work one day and not the next...cooling systems are a real pain in the butt. when air gets in them through leaks your idle will be rough.. you can have heat one minute and nothing the next if air is stuck in the system..i dont know the age of your radiator but look at it they can seep antifreeze and u wont necessarily see it. check around the filler neck and where the plastic tank attaches to the radiator frame.. they tend to crack right at the top vibration off these old cars can do this, sucky motor mounts.. i went through a thermostat, stuck closed, a heater knob no heat, then finally the radiator had to be replaced. water pumps dont kick on and off.