07 5.3 flex fuel - engine oil

[mhgoldwing]

Owners Manual states that ONLY 5w-30 weight oil is to be used in this engine. Never seen this limitation before. Guess it has to do with the aluminum engine block or something. Anyone know why?

P.S. 07 1500 Suburban 4x4.

[Steve]

I read a bit about it. I think there are several reasons, but I don't recall off the top of my head.

[Toymyster]

The newer engines, having tighter tolerances, require thinner oils. It has to do with the newer, more precise manufacturing technologies, and the fact that thinner oils help better fuel economy. My Bimmer, for example, require 0w-20. I don't know if your truck requires it or not, but I would definitely use synthetic oil!!