A few people asked me if using AMSOIL as directed will void their warranty. The short answer is:
Absolutely not.
The long answer is:
The Magnuson-Moss Act (in the USA) protects consumers from being denied warranty service by the manufacturer of their vehicle for a modification that was made unless they can prove that the modification caused the failure for which the warranty claim is made. For example, if you change your radio, they cannot deny the warranty on your suspension, and if you put in a performance air intake, they can't deny your warranty on your transmission.
AMSOIL's recommendations carry their own guarantee. Within reasonable limitations, the use of AMSOIL's products as directed and recommended by AMSOIL through their product guide carry a warranty protection for the duration of the recommended interval. If the lubricant is found to be defective at the time of a failure, AMSOIL will replace the lubricant and, at their discretion and expense, either replace or repair the defective component. For example, AMSOIL recommends 2x severe service intervals for their Signature Series ATF, which is 90k miles in our cars. If, at 80k miles, the transmission suffers a failure and GM blames it on the fluid (assuming they somehow found out you changed it), AMSOIL would test the fluid to determine if it was still usable. If the fluid is found to have ample life remaining and within the specifications required by the OE fluid, GM will be required to perform the repairs at their expense or face a lawsuit they cannot win. This also adds additional warranty protection to your vehicle once it has passed out of GM's warranty period.
Of course, there are exceptions to these rules when it comes to oil drain intervals. If AMSOIL recommends a 90k mile severe service interval and your Cruze is tuned and has significant bolt-on modifications that increase power, it is safe to assume that you will need to change the fluid more often than recommended by AMSOIL to maintain that warranty.
If a dealer so much as suggests that the use of an AMSOIL product will void your warranty, let me know and I will send them a stern letter reminding them of the laws that they are required to operate under. They have no legal authority to deny any warranty claim for the use of an aftermarket product. That action can only be taken at the time of a warranty claim if it can be proven that the product caused the failure.