I have a 2004 chevy Monte Carlo SS. It keeps over heating

It had a clogged radiator. I flushed it with a water hose for over an hour. The water was
pretty clear when I stopped. I drove it from Macon to Savannah with no antifreeze. It did
not run hot. I flushed it be caused when I checked the radiator it was still muddy looking. I
actually flushed it twice with engine flush and twice with just water until the water was
clear. I then changed the thermostat. It still overheats, the temp gage goes from normal
to about 210, it never gets higher than that, I'm afraid to drive it far because I don't know
why it keeps getting hot, what do I do??