At 04:18 PM 4/3/2008, Bob Stevens wrote...
>If the container says SM on it, it's zincless; and must say SJ (?) to
>be safe?

It is not that simple. There is no limit on zinc in any of the grades.
There are limits on phosphorus, which limits the use of ZDDP (zinc
dialkyl dithio phosphate), which is the antiwear additive that people
are concerned about.

API SJ has a "non-critical" phosphorus limit of 1000 PPM (0.1%) for
0W-20, 5W-20, 0W-30, 5W-30, and 10W-30 weights. It must pass the wear
test of ASTM D 4485 Test Method Sequence VE.

API SL rated engine oils required minimum 800 PPM phosphorus (as part
of ZDDP), _or_ a pass on the wear test mentioned above. It has the same
"non-critical" phosphorus limit as SJ.

The API SM spec has a phosphorus limit of 800 PPM, for the grades given
above. Other weights have no limit on phosphorus (or zinc). All weights
require a minimum of 600 PPM.

None of the weights with a phosphorus (and consequently a ZDDP) limit
are suitable for a VW aircooled engine. For the weights which are
suitable, there is therefore no way to tell from the API grade how
much, or how little, ZDDP is present, except that SM requires a minimum
of 600 PPM (which is about 1/2 of what was typically found in the old,
"good," oils).

In short, without an oil analysis, you can't tell.