Stripped bleed valve
 

I have a 2007 300 Touring and just put in a new thermostat, fan assembly and got a new water pump today to install. I've been refilling radiator with water and bleeding regularly to avoid overheat. However, I managed to tighten the bleed valve a little too tight and now I've rounded it out. I cannot unscrew it, it's stripped. Any advice? Having trouble finding a new bleed valve screw but not sure how to loosen this one.

I don't know the engine fully on that model but where is the bleed valve?

If it's on a pipe, just replace that pipe.

I would suggest drilling it out but you run the risk of contaminating the cooling system with debris then. You could try putting a nail or something similar into the current bleed valve screw and removing it using that with a pair of pliers.

Be careful though as you may have damaged the actual screw hole by over-tightening the original valve screw and due to that being damaged may not be able to get a new one, so will end up at my original suggestion of replacing the part that the bleed valve is on.