Coolant system

Had a radiator leak, sealed it with a stop leak. Weeks later radiator stopped dripping, so I went with a new one, now I have no leaks, but car runs hot, when driving the needle kind of stays around the middle, when I come to a red light or stop sign needle works its way up. I pull off it goes back down eventually it reaches the hot mark; I was told it might need bleeding (coolant system). So, I opened valve it's shoots a little coolant but at the end of it all it's just hot steam coming through it, change the thermostat and housing still runs hot sitting still, before the radiator replacement I didn't have these kinds of problems, car was just fine. Can someone point me in the right direction? I need my car for work. Thanks