Radiator and Coolant overflow

Just wondering how the radiator works with the overflow tank……first off here’s what’s going on… I’m not overheating, I’ve changed my thermostat, and also recently changed my intake coolant hoses…… so I’m not leaking any fluid……

But the problem is after a long drive it seems that the coolant is being sent to the overflow like usual, but it does seem to return back into the radiator… it just fills up the overflow and boils over and out…so what’s going on here……is my rad starting to go…