Originally Posted By: Wicked94Z
... The usual responses I get when I tell people I run 10w30 is "In a 7.3??? Say goodbye to your turbo! You can only run 15w40!" and a lot of head shaking.
Generally, the prejudiced notion is that thicker oil is important for film-thickness under high bearing loads (crank and rod journals). I certainly agree that a minimum thickness is important, but wear data clearly shows 10w-30 is "thick enough" in many, many applications, and even in the 7.3L.
Why the turbo in a 7.3L would be affected with respect to vis is beyond me; it sees no such loading like the crank and rods. As long as the hydrodynamic barrier is present, the film strength really isn't a major player here. Their fears are unfounded and based upon rhetoric IMO. I'd file that under "poppy-cock" until they could produce solid evidence.