I have been using Mobil Delvac 15-40 in my sideoiler since built.
My understanding is that over the past several years the
oil companies have been ordered by the EPA to remove
zinc additives from their automobile oils. In doing so, they have significantly decreased the wear-in properties that
zinc provides, particularly in older types of engines - in my case an FE. Diesel oils such as Delvac and Chevron Delo still contain significant amounts, however.
I have heard many builders recommend that motorcycle oils be used during break-in, as they still continue (although decreasing) to contain the
zinc additive. Word is, they too will lose most of it as time passes, again due to EPA rules.
Several months ago, I stumbled onto a study done by an independent testing lab that showed the content of zinc and ash in currently available motor oils. I don't recall the web site, but a search should lead you to it.
My .02 cents...
Bud
