on the way home today while sitting at a red light i noticed that the engine temp begain to grow but once i started traveling again it went back down to normal temp then the next red light a long one (about 1-2 mins) the engine temp went all the way to the red line before i shut it off and waited for the light to turn green. after a 30 min drive down the interstate on the way home everything seemed fine but once i begain idleing again in my parking lot the temp started to rise again..... what could be causing this i check and both the fans were running and oil level is fine (ill change it tomorrow just incase) the engine is to hot for me to check the radiater fluid but i have never had problems with it leaking (ill check it in the morning)

its a 91 stock ls with 112k belt and water pump was changed at 90k

i am a broke college student and this is my only car that i need to get to school any suggestions? thoughts? comments?

thanks