A friend goes into a local dealer to get the first service on his new vehicle. At the parts counter he purchases Amsoil. At the service counter he presents his Amsoil. The service writer informs him that Amsoil will void the manufacturer warranty because the manufacturer's synthetic oil is "thinner and splashes onto the bearings better".
My friend calls bullshit and then, at the end of the discussion, points out that he bought the oil from the dealership.
My friend is a petro-chemical engineer with thirty years of experience working in refineries.
Wrong person to try to peddle your BS to. Service was performed with Amsoil.
Next day, picking up the finished vehicle, service writer has nothing to say except "your vehicle is ready".
My friend will never have that dealership work on any vehicle he owns. Ever. For any reason including warranty.
Sometimes if you don't know anything you are better off just keeping your mouth shut instead of making something up and getting called on it by someone who actually does know.
Names omitted because it doesn't matter.
Update: Talked to the guy at the parts counter who is not a know-it-all jerk and he gave the accurate story. Harley Davidson has decreed that heavy weight oils are not appropriate for their six speed transmissions. These will have their warranty voided if they fail and it is found that the customer has been using heavy weight gear oils (standard for all the five speed transmissions for years, by the way). I guess the service guy heard just enough to draw exactly the wrong conclusion. Maybe he needs to pay a bit more attention in the meetings or read the literature a bit more carefully.