overheating

NO, they tend to creep up in temp setting at a light with the car in gear( auto) or with the ac OFF. Until you reach 220 deg, you are fine. These engines are supposed to run hotter than the older ones. That's what burns off all of the water out of the oil, and gives you that great mileage. That's why you run synthetic motor oil ,to protect the engine from the heat. The computer will do the rest, it has a protection mode if things go wrong.

No, but synthetic oil is not always needed either. In '89 most engines were not designed for synthetics, a good petroleum oil changed regularly is fine, maybe even better, if the engine has not used synthetic since new, changing to it later can cause leaks.