It wasn't written in my owner's manual, or anyone else's for that matter. The service manager has paperwork from his Toyota Regional Representee-Toyota Corporate, where it is written. I doubt if Toyota will have it on highway billboards stating this. I assume the 0w-8, 0w-16, and maybe the 0w-20 are more related to increasing fuel milage (CAFE) than promoting the longer life of the internal engine parts. I may be wrong here, for all I know racing people are running 0w-8 engine oil in drag race engines now because it protects better than 20w-50. I just know 0w-16 seems thin to me, it doesn't mean it won't protect as good as a 5w-30, I guess. I am not a college educated mechanical or chemical engineer. I mean, 0w-20 really is not much different than 0w-16, it just feels a little better. Hell, if the guy would have said I could run 5w-30 in it with no warranty issues, I would have felt so good I would have had to sit on my hands to keep from waiving at everybody. Maybe the guy just told me that to shut me up, if that is the case, it worked. Later, Joel