Well fuel dilution is a totally different subject. I would be even more cautious with fuel dilution. If your fuel dilution is causing your oil to drop out of grade, the change interval should be adjusted to compensate for that to avoid that dilution compounding the issue.
The bottom of the SAE would certainly be my limit for viscosity loss if fuel dilution were the culprit. I would much prefer my oil to shear out of grade rather than be diluted to a lower viscosity.
If you have an irremediable fuel diluting engine and are aware of that fact, I would suggest starting with a higher viscosity oil from the start unless you are closely monitoring it and are changing it frequently. I certainly would never suggest using an oil that is already close to the lower limit of the recommended viscosity in that case.
The bottom of the SAE would certainly be my limit for viscosity loss if fuel dilution were the culprit. I would much prefer my oil to shear out of grade rather than be diluted to a lower viscosity.
If you have an irremediable fuel diluting engine and are aware of that fact, I would suggest starting with a higher viscosity oil from the start unless you are closely monitoring it and are changing it frequently. I certainly would never suggest using an oil that is already close to the lower limit of the recommended viscosity in that case.
