2006 dodge magnum 2.7 overheat/ no heat. help

have a 2006 2.7 dodge magnum. my radiator got a crack in it so I replaced with new one the car never overheated anytime now I have no heat, and one I go only a few miles the car overheats very fast.
I had a problem last winter of the heat not working on and of while at idle. noone could figure it out.
after replacing the radiator, I did bleed the air out of the system. I can start the car and leave running at idle and the car won't over heat..
I see no leaks, no knocking or smoke etch anyone have any ideas what it may be??
also the fans work fine.
thanks in advance for any info