So after the LS sat for 4 weeks. I decided to start her up again today to see if I could easily repeat the overheating that made me park it in the first place... After running about 20 minutes this happened. I ordered the replacement thermostat and a new gasket today. The fan ran like crazy, but couldn't cool the car. (Also, not much heat was coming from the radiator) The degas bottle nearly filled to the top with fluid after it got hot. Everything seems to be in running condition, so my next step is to replace the thermostat. $30 for Motorcraft thermostat and gasket doesn't seem bad to me. I hope this is my only issue. I wish I could flush the system as well.