Only the manufacturer of an engine can adequately determine what type of
  oil to use during the break-in period.  They have first hand knowledge
of the parts and assembly techniques used in the engine in question.
Odds are that they will repeat what Mike is saying, which is to use
conventional motor oil until operating temps, fuel economy, and oil
consumption stabilize.  A few manufacturers have assembly techniques and
can specify (more like manufacture for themselves) parts that are
appropriate for engine break-in on synthetic oil.  You cannot correctly
infer that all engines can be run on synthetic during break-in.  And no,
Terry, the waterboxer is not a "modern" engine.  It is a part of
automotive history that we are now stuck with because VW made the
Vanagon engine deck too low to fit a Chevy V6 in there without serious
body modifications.

Mike Snow

Terry K. wrote:
> Oh--a modern engine--eh Mike--?
>
> What in the hell is a Wasserboxer?
>
> Flatthead Ford?
>
> Oh maybe a Briggs and Stratton?
>
> Koehler?
>
> Wisconsin?
>
> What is you defininition of modern?
>
> Anything that was built after the Vanagon
> engine?
>
> Mikey writes;
>
> Don't know but maybe these modern engines were designed to work with
> syns?
> mike
>