i always run my engines on fully synthetic oil unless there is a pacific reason not to
some older engines were not that good and oil would leak out due to the oil been so thin (I'm talking about other makes of car not Vw )
i prefer to run them on fully it protects the engine more , keeps the engine cooler whir increases the overall performance you may not see it or feel it but it you dine a vehicle with semi and fully synthetic there is a difference on the charts
i work in the bike industry and i deal with a big bike oil supplier the stuff they can tell you is unreal oil is not just oil its all the additives and the quality of oil when bought makes a good oil
if you can find rock oil (brand) in a car oil please let me know very good brand british made and i swear by the bike oils
