did it just start overheating after u flushed ur cooling system? if so u probably have air in it. i dunno about 240s but there might be bleeder screws on ur car for the coolant. id say do that and check out the thermostat first. also if u just put a new thermostat in and it has a little hole with a dangly thing in it, make sure its facing up. it could be other stuff too but id probably check that stuff first and then move on from there.