Some myths about using synthetic oil are that once it is used in a car the car can't use natural oil again, synthetic oil cannot be used in old cars, and synthetic oil improves fuel efficiency. Another common myth is that synthetic oil causes oil leaks.
Switching between synthetic oils and natural oils does not damage a car. Also, synthetic oils work just as well in old cars as they do in new cars. Synthetic oils do not improve a car's fuel efficiency and are not any better for an engine than natural, conventional car oils. Synthetic oils do not cause oil leaks, but they can clear up old oil deposits, which may expose pre-existing issues.