Does it harm yor car to switch between regular and synthetic oil?
If the vehicle requires that synthetic oil be used, I would recommend always using synthetic oil. If the vehicle does not require synthetic oil, I would only use what is required as money can be saved throughout the life of the vehicle by not buying high dollar oil when you dont need to. That being said, if synthetic oil has been used, it is ok to switch back to regular oil. However, I would not recommend switching back and forth all the time. Choose one type of oil and stick with it. Switching back and forth between regular and synthetic oil can cause the vehicle to burn or leak oil.