Must I use synthetic oil?

If your car is still under factory warranty and you don't want to void that warranty - Yes. If the car is out of warranty or you don't care - No. although it is highly recommended that you do use synthetic oil as specified by the manufacturer to ensure the best life and performance from your car. compared to a new engine the cost is negligible and you may see a decrease in fuel mileage using conventional oil. If you choose to use conventional oil and you do have a warranty issue the dealer will have your oil tested to make sure it meets the warranty requirements.