Well without looking at the vehicle its hard to tell exactly whats wrong. No heat and overheating with antifreeze in the system is usually a result of blown head gasket witch could be why your oil is over full. Also those 3.8 engines are bad to blow the upper intake gasket and loose coolant...
take it to a shop and have it pressure tested unless you have the ability to seal and pump up the radiator to 15psi MAX and look where its spraying from. Under the water pump pully is a small hole visible from underneath. get a flashlight and see if its leaking from the weap hole. Could be a...
You can put whatever kind of exhaust you want on it but keep these things in mind. Your car has a converter and O2 sensors so removing them will cause the engine light to come on and in some cases rough running and poor economy. If its the GXP with the V8 then I'm pretty sure flowmaster has...