Wa Alaikum Assalam,
bhai, agar apki car heat up hoti hai summers main, tab aksar mechanics radiator service k baad thermostat valve remove kar detay hain, is se engine heat up honay ka khatra "thora sa" kam hota hai.. kyon k car ka engine normal operating temperature per pohanchta hi nahi is liye heat up bhi nahi ho pata jaldi...
lekin iska nuqsan ye hai k engine k RPM lowest possible setting per set nahi ho patay properly garam na honay ki wajah se.. lehaza engine fuel thora ziada khata hai phir ...
bottom line is, if your car has a history of engine heating up and the previous owner has removed the thermostat valve, it is probably because of the reason the car heated up and mechanic removed thermostat valve... if it is like that, keep it like that until it's running fine... if you will fiddle with it now, be preparde for lot more expense.. like you will have to get radiator serviced, all hoses checked for leakages, and then get new thermostat installed...
as company fitted settings, all cars have thermostats installed in them ..
hope this helps !