Originally Posted by sykozis
Whether a lubricant meets the manufacturer's lubricant specification or not, the warranty can NOT legally be voided as long as the proper oil weight is used.
That's only partially true. It's not the weight, it's the "oil spec". Each vehicle has it's own oil spec. BMW has LL-01 while some Ford vehicles may require WSS-M2C937A. Even if both oils were the same viscosity, you could not interchange them. A warranty can only be voided if the WRONG oil spec was used. The Magnuson-Moss Warranty Act
makes it so that you can legally use any oil you wish as long as it meets the manufacturer's specs. If the manufacturer "requires" you to use a certain brand oil, then by federal law they are required to provide that oil to you free of charge, per Magnuson-Moss Warranty Act.