bro, not arguing here....we're here for a reason. to discuss & find solution :0 so if i offended u any how, im sorry.
back to the topic. ermmmm, i really have no idea y shell advice users like that. but i've came across other sites that says to use a thicker viscosity oil for older engines, due to the gaps being wider after wear & tear & newer engines or new design engines that has tighter bearings can use lower viscosity oil. so this sounds more logical, instead of saying use fully-syn for new engine, semi-syn for old engine, mineral for older engine. doesnt make sense, coz its the viscosity that we're interested abt, not its base stock.
back to the topic. ermmmm, i really have no idea y shell advice users like that. but i've came across other sites that says to use a thicker viscosity oil for older engines, due to the gaps being wider after wear & tear & newer engines or new design engines that has tighter bearings can use lower viscosity oil. so this sounds more logical, instead of saying use fully-syn for new engine, semi-syn for old engine, mineral for older engine. doesnt make sense, coz its the viscosity that we're interested abt, not its base stock.