Could using AMSOIL Synthetic Motor Oil void your vehicle warranty?

Absolutely not: Vehicle manufacturers recommend using motor oils meeting certain grades and American Petroleum Institute service requirements. Whether the motor oil is petroleum based or synthetic will not affect warranty coverage. The manufacturer is required to cover all equipment failures it would normally cover as long as the oil meets the requirements and was not the cause of the failure. AMSOIL exceeds these requirements and has never been deemed the cause of an engines failure. Even so, AMSOIL has its own limited warranty, protecting you even further. In addition, the Federally mandated Magnuson-Moss act states that a manufacturer may not require the use of a specific brand of aftermarket product unless it is provided free of charge.

This also applies to aftermarket parts installed on your vehicles. The manufacturer must prove that the part that you installed caused the damage. An example would be an aftermarket high performance mass air flow sensor. If your engine is damaged or you have an emissions problem and your aftermarket part did not cause the damage, the dealer/manufacturer can not void your warranty.