my 300m boils over after i shut the engine down but as ong as i drive it its fine and never overheats

What temp does it run at when cruising down the road? Do you notice any oily residue in the coolant overflow? You might want to get a radiator cap that has a built in thermostat. You can compare that temp to the dash dial. How much of the coolant gets pushed out? Try taking radiator cap of with car warmed up,but no pressure in the system. Rev the engine slightly. You should notice the coolant level go way down and then as you release the throttle the coolant should overlfow. This will show condition of coolant pump.

The temp runs right below the halfway point on the gauge. When I pull the cap and rev the engine the level goes down but not very far. I have a lazer temp gauge the car runs right at 197.3 most of the time. I think I might have found the problem Last time it blew out the water when I refilled it after bleeding the air I would squeeze the radiator hose and more air would come out I jacked up the car so the air bleed was the highest point and poured water in to the bleed till it would not take anymore it has not lost any water since but I have not driven it far enough to really give it a good test. Thanks for the input.

U probably need to bleed the coolant system

I have the same problem sometimes it don't overheat. I changed the t- stat but still over heats but not all the time. I watch to see if coolant is flowing and it is but still overheats.

Finally found the real problem the radiator had a very small leak on one of the tank seals when the system would cool down and the antifreeze contract it would suck a small amount of air into the radiator instead sucking water from the overflow tank the system would get an air lock and overheat. put a new radiator on it problem solved.

With my 2001 Chrysler 300 m I just had the problem of boiling after turning down the engine Solution was radiator cap replacement that's thanks to this cargurus and the people who post experience here I also did the bleeding from the top of the engine but it's works better with engine hot just be very careful Hot gasses will come out