baka clogged na ung ibang parts ng radiator mu or baka marumi na ung bottom part ng radiator kya ayaw mgflow ng maayos ung water.. try full draining the water
put running water so that it can help cleans the radiator

pag di pa din ok yan overhaul na ng radiator need nyan or a new 1

is the other fan working well? check mu din baka di na cya ngautomatic