Ford mustang 2001 v6 3.8L code p1285, overheating, radiator leaking?

My car has the p1285 code. Radiator pukes from the bottom.
I refill radiator and temp is stable but overheats as the water drains from radiator.

-I replaced thermostat
-belt is good, running
-no leaking from hoses
-fan works
-no leaks from anywhere else.
-AC works

What could it be? Bad sensor?

Thanks in advance!

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