It is possible the thermostat could be stuck open . That could mean the thermostat is faulty . Hasn't happened to me in a while but it has so I still keep that in mind if this should happen .
eventually , after a long drive , the engine coolant gradually gets hotter and doesn't cool efficiently . Not good for the engine . Thermos must close when cooler engine coolant from radiator circulates to engine and opens when engine coolant gets too hot. That is proper circulation and proper cooling system operating.
Yes , getting the air bubbles out is necessary to prevents hot pockets . That air pockets that get trapped in the engine . That will send the temp gauge up . I believe in your case the thermo is not closing . I'm sure the thermo and gasket is installed correctly or you would have found a massive leak already . That wasn't the case for you , thankfully . Hate when that happens , the thermo slips out of place when closing up the housing . We always got to be on guard for it . Too bad we can't turn the jeep on it its end so gravity can do its job .
