put a new 180* t-stat in the car 160* will be too low and a stock tuned computer wont let the car run properly, your stat is hung wide open or one is not even in there at all, i had this issue when i found out the genius i bought the car from took it out and never replaced it =\

 

A 160 wont hurt anything, I ran my car like that for years. His car is overheating, so it cant be that there isnt a thermostat at all either. The fact that when his fans come on the engine cools tells you that the whole cooling system is ok, and that is a control problem not turning on both fans.