I am a firm believer in synthetics ( other than Syn3 ). I used Amsoil for years and never had the first issue, so I'm not knocking Amsoil's produts at all, just got tired of haveing to order the stuff all the time and pay shipping costs. Maybe it's me just getting older & not wanting the hassle but I changed to M1 cause it's readily available to just walk in the store, pick it up, come home and change my oil.