318 is not hot enough

So with my duster project finally finished with a rebuilt 318 beefed up headers and etc I also baught a new champion performance radiator 26 in 3 row aluminum. My problem is that the radiator does such a good job that my engine runs around 150 degrees no hotter or cooler and my thermostat is a 180. So with that said is it a problem with the water circulation not fully circulating because the thermostat isn't opening or should I downgrade my thermostat to 140 or something like that. Other then that it runs grate thanks for your help in advance