I am a dealer of Amsoil Synthetic lubricants, have been for nearly 20 years and there is no required break in necessary on the engine. Amsoil is the only oil out on the market that boasts an extended drain interval and backs it up. Naturally, I agree with the other responses that the suggestion is to use synthetic because of the chemical properties inherent with them vs petroleum. In the case of Amsoil and extended drains, the question concerning warranties usually comes up and Amsoil has you covered. I've done the research on the other oils out there but I've personally never found anything that comes close to the synthetics, especially when you take look at Amsoil and the filters they make.