Double Check if yung thermoswitch na pinakabit mo is yung para talaga sa vios mo,

if it is, you could try replace your cooling system's coolant with a fresh one,
and check also your cooling systems thermostat, might be ndi na nagbubukas sa tamang
heat range nya.

medyo alanganin gamitin yung kotse madalas magblink ang overheat lamp.