Running hot after partial coolant change

Inevitably it corrects itself. In my experience the closed system pressure slows that process down.
BTW. When checking or removing hot radiator caps. Always squeeze the upper radiator hose first, if that is soft, theres little psi behind the radiator cap, and its safe to open.
If that upper hose is hard, theres alot of psi in that radiator and WAIT to open the cap.
Take care.