Getting back to the OP's question, assuming you aren't measuring it yourself, I'd think you'll get fuel dilution measures as part of a UOA which will also tell you the viscosities.
The viscosity dropping below that specified by the manufacturer would perhaps be a reasonable basis for oil change.
In practice I'd think the lab supplying the analysis will probably advise you on this.
The viscosity dropping below that specified by the manufacturer would perhaps be a reasonable basis for oil change.
In practice I'd think the lab supplying the analysis will probably advise you on this.
