I recently had a good clear out of my garage and found 3 x 1 litre bottles of castrol magnatec car oil that i had got free over the years with larger 5 litre bottles, the grade is 10w40 which i think is fully synthetic, not trying to be a cheap skate but do you think i could use this for my next few oil changes, my manual says use 15w40 or 10w40 mineral so this being fully synthetic im thinking its got to be better than any mineral oil even tho its bottled for car use, do you think there is really any difference in motorcycle and car oil. At the moment im running castrol 10w40 4t racing fully synthetic, it just seems a waste of the magnatec if it would be fine and who knows with its cold start protection could even be better, has anyone else used oil bottled for car use.....