P0597 Code

The only reason I'm even posting this is that I just replaced the thermostat and manifold it mounts to a month ago with a brand new Dorman part. I'm going to clean all the connectors since the coolant got everywhere when the old manifold cracked after replacing the thermostat. The car is running fine and temp went to about 134 degrees just idling yesterday. While I know the thermostat is 221 degrees, with the engine size I can see it may not go up to that unless under load. Anyone else dealt with this recently? I saw posts on models from before 2010 and the Haynes book is lacking in most areas I've tried to look up so far.