We know they make great oil but which products won't void your warranty if you have a major engine /tranny/diff claim? The Xl 7500 series are currently certified, but what about any other oils, gear lubes, pre mix? Amsoil warrants it's product if used as directed and I'm sure it would do no harm if you follow their guidelines, but your XXX brand car or equipment dealer will likely say otherwise if an engine blows at 20K under warranty when he or the head office hears you used that "snake oil" stuff from Wisconsin in your engine instead of good old OEM etc. I would imagine Amsoil would test ok on analysis so their product held up, no warranty from them, and the car is wrecked with an unaproved oil used so no warranty from dealer. Even though it is likely their part failed but how can one prove it would have or would not have happened with xxx brand approved oil instead. Amsoil claims it is expensive to have oil formulas certified which is probably true, but I notice buck a quart no name stuff in the department stores that has a starburst symbol from API. Is this to say that the big oil company that bottled the cheapo stuff only neads one approval for that formula no matter who sells it under whatever name? Also do we need to change our oil at their mile time guidlines and filter too? What about filter brand. Magnuson Moss covers the brand issue but is their a standard like with oil. (You can use any kind you like if it meets these specs etc) What about viscosity if the say 5W20, can you use 5W30,10W30,20W50,SAE60, if they have an SL or SJ stamp?