Need advice-Temp. keeps rising

[ndestree]

So my Car runs fine. I just instaled a new radiator and all was well and at idol it runs perfect, but when i start driving the temp. starts to rise unless I have the heater on it rises. With the heater on though it stays at half (perfect), thermostat? water pump? I'm not sure anyone else have this problem

[Daox]

I'd start with the thermostat. Its cheap and easy to fix.

[NickR]

Just double-check that the coolant level is full. It's easy to get air in the system when replacing a radiator. If that's OK, then yes, as Daox recommends, replace the thermostat. If that doesn't fix it, try a cooling sytem flush. Only if that fails, look at replacing the water pump.