Over the years it has been my observation that oil changes (of the same exact type) result in less MPG early on. Then as the oil milage increases, the MPG gets back up to normal for each car. Then it stabilizes for the remainder of the oil run. Have you noticed the same? Sure, fuel dilution can do this but many cars do not have this problem. And rapid "shearing" can do the same. But many oils are very shear stable.
Engine manufacturers certainly know this and specify viscosity grades accordingly. In Ferraris the spec'ed oils routinely drop a grade or two within a few hundred miles. The specified 60 grade Shell oil in the Enzo dropped to a 40 grade oil almost immediately. Every 40 grade oil for the other cars drop rapidly to 30 grade oils then stabilize there.
Thoughts?
Ali
Engine manufacturers certainly know this and specify viscosity grades accordingly. In Ferraris the spec'ed oils routinely drop a grade or two within a few hundred miles. The specified 60 grade Shell oil in the Enzo dropped to a 40 grade oil almost immediately. Every 40 grade oil for the other cars drop rapidly to 30 grade oils then stabilize there.
Thoughts?
Ali