supra help

hi i have an 89 turbo bone stock 5spd turbo.. my problem is when i start the car after its been sitting so obviously its cold it'll warm up and then after driving for a while whether highway or city it'll start to overheat get to the redline (H) and then just start to drop dramatically to slightly above half for a few miles and then do it all over again?? Just before it got to the redline i popped the hood and was feeling on the top rad hose and revved it hurt something like whistle and then the hose got softer and the temp dropped to under halfway.. Any help suggestions... My guess the T-stat.. another thing is at around 3500-4500 RPMS u can actually here water going through the system?????

you ethier have a bad thermostat or a leaking radiator. pressure test the colling system and make sure nothing is leaking out. then crank the car cold and what till you hear the thermostat open, if you don't hear it that would preobably be the problem. if the pressure test finds any leaks fix them and try the cold crank again. It might not be a bad idea to get the cooling system flushed to make sure there is no trash blocking anything. Hope those ideas help.