engine temp. problems to

My wifes car gets extremely hot, like some others that I have read aobut.Its a 98 aurora,the thing is I'm not sure if replacing the thermostat is going to help. The fans don't come on until around 240 degreas and I asked a machanic and he said that there is no way to reset when the fans come on. If they came on like some people are saying, around 210-220, maybe things would be ok. would someone tell me if I need another machanic, can this problem be corrected.:uhoh: