1999 Subaru Legacy Wagon 2.5GT 167k miles, recently we replaced my radiator because it broke and now at random when stopping and idling, my temp gauge will rise up and if i rev my engine up it will drop, but sometimes it will not drop and continue to rise, if it rises to H it will spill coolant through the coolant reservoir, when the gauge is rising there is also little heat coming out of the air vents. I am suspecting an air leak in the coolant system or a faulty thermostat, i do not think it is my radiator fan because it works properly and this issue did not happen with my old radiator.

Other note: when starting my car cold, you can hear an audible sloshing noise in the vents, that's why i think its an air in the coolant issue but we have tried bleeding it out multiple times and it still has not fixed the problem.