Replace rad cap, thermostat (and gasket), flush and refill system, check the fan and clutch that they actually work. When you flush and fill, make sure to "burp" the system, or you will experience problems. If none of those things work, check to see if the guage and temp. sending unit work properly. If they do, replace the radiator as suggested. Also, check to see if your heater core is leaking and there are some hoses that are hard to see, I had one underneath the thermostat housing crack and leak down the hose and drip no where near where it was actually leaking from, PITA to find. Good luck!