I started the car and automatically it went to 150F. After it warmed up, it went to about 230F. It was about 70F today and no one started the car today. The antifreeze has been flushed (about 2 weeks ago). It's a 2004 SS, Its operating normal now (mood swings?), but just curious.

 

Sounds to me like you had a momentary sticking of the thermostat. Might be a good idea to replace it. Pretty easy job. They sell a fail safe thermostat now that will fail open and not cause your engine to overheat.

 

Thermostat is actually brand new haha.

 

Temp sending unit (not sensor) starting to fritz out?