[aerohead]

As I understand it,all synthetic oils have viscosities which are actually lower than what is listed on the label.They are not permitted to advertise the lower viscosity,however,they flow more freely when cold,than a straight mineral oil of the same label rating.So for cold starts especially,pumping losses are reduced,and fully-warmed viscosity is no lower,and do offer slight savings.Synthetics have been claimed to swell seals,and it has been claimed that if you switch to a full synthetic,then switch back to a straight mineral oil,you run the risk of oil leaks.