Everytime I use a different oil, I smell it before I put it in. I don't know why and I know it probably doesn't mean anything. Here are my recent observations: Havoline - smells mineral oil, they all smell the same. Mobil Drive clean - smells mineral oil Mobil1 (tri-syn) - almost has a kind of sweet smell. MaxLife - can hardly smell a trace of mineral oil. It also has a somewhat sweet smell. Royal Purple - Smells mostly like a mineral oil The reason I posted this is I'm now curious as to what synthetics have a dominant smell, or is the differences in the additive package? From my testing (if you call it that), I'd say that esters have a dominant smell. But what about PAO's?