1974 Other Ford Models Engine tempareture run away

Engine Cooling problem
1974 Other Ford Models V8 Two Wheel Drive Manual

Dears Sirs,
my name is Anthony,
I have an old gravel truck with a FORD 429 V8 engine in it.

my prblem with the enige is that when I switch off the engine the temperature instead of stay at that range and start comming down slowly, it will increase and than it will start coming down( ex: if engine was stopped at 202 F, it wil go all the way to 230 F, than will start coming down slowly).
I have clean radiator, take thermostate out, to see if it keep doin the same, but its still the same.

can you guys tell me what is happening and how to address this problem.

Sincerly, Anthony.