No, the 6 months recommendation is due to absorbed water vapor causing gelling and sludge. It's specifically targeted at vehicles that aren't driven often, or

No, the 6 months recommendation is due to absorbed water vapor causing gelling and sludge. It's specifically targeted at vehicles that aren't driven often, or only take short trips. In these vehicles the inevitably absorbed water is not driven off by engine heat often enough and they become fouled due to sludge. The mileage based change intervals are about two kinds of degredation, shear (loss of viscosity), and Ph (exhaustion of wear additives). Shear may be improved by synthetics but additive depletion is not, although it is uncommon to run oil long enough for that to become critical.