Thermostat valve is removed or bypassed when car cooling system failed to keep it at optimal temperature and rises the temperature. So Desi mechanic simply remove the T valve.
Majority of people who don't maintain their car uses tap water in radiator which ruins the engine and radiator in long run.
Due to excessive over heating Head gasket gets damage easily.
Hope so head gasket replacement and radiator cleaning will solve the issue.
And last thing how previous owners sells you the car by claiming it 100% genuine will definitely get the Reward in this life or hereafter.