Reposting with a title that will make sense in the archives.

Jim

On Jun 4, 2011, at 10:06 AM, David Beierl wrote:

> At 11:09 AM 6/4/2011, Dennis Haynes wrote:
>> With today's modern oils there is no reason to have to go to the
>> straight 40 for any temperature. I don't even know straight weights
>> are available with the latest specifications. 20w-50 or 15w-50 will
>> work just as well.
>
> But you agree that 15/20W50 is correct oil for *all* WBX in cool to
> very hot temps?

I would, with a caveat.

In the case of motor oil, newer is not better. As engine technology
has advanced, motor oil specifications have also advanced.  The 20W50
GTX today is a significantly different product than the 20W50 GTX that
was on the shelf when these VWs were new.  One of the major
differences that directly affects us is the reduction of certain
additives that were designed for flat tappet engines. Primarily zinc
dialkyldithiophosphates (ZDDP). Do not use engine oil with the "SM"
rating. Or, if you're going to use engine oil with the "SM" rating,
use a zinc additive that will maintain proper ZDDP levels.

Quoting wikipedia, "The main use of ZDDP is in anti-wear additives to
lubricants such as greases, gear oils, and motor oils, which contain
about 1%. For applications in oils for gasoline engines, zinc and
phosphorus emissions could damage catalytic converters and have had
their quantity reduced in standard formulations.[3]. Reduced ZDDP oils
have been cited as causing damage to, or failure of, classic/collector
car camshafts and lifters with flat tappets which undergo very high
boundary layer pressures and/or shear forces at their contact faces,
and in other regions such as big-end/main bearings, and piston rings
and pins."

A quick Google will take you to way more info than you want. Just let
it be said that less (or no) ZDDP in the current crop of off the shelf
motor oil is NOT good news for us.

Personally, I use Shell Rotella T synthetic 5W40 in every internal
combustion engine I own. From the F350 to the 4 stroke string trimmer.
<http://forums.pelicanparts.com/porsche-911-technical-forum/435355-zddp-shell-rotella-t.html
 >

This is a decent examination of the issue: http://www.ttalk.info/Zddp.htm

Jim