I wrote:

I have been using Mobil 1 oil, 0W-40 grade, in my '96 2.4
Diesel Transporter, almost since new. Originally, this oil
satisfied VW specs 500.00 and 505.00, as recommended in the
handbook for this vehicle.

Over the last few years, formulations of this oil claim
testing to VW 502.00, 503.01 and 505.00. I understand that
502.00 supercedes 500.00, and that 503.01 relates to longer
drain intervals with "smart monitoring" of driving patterns.

Interestingly, I came across a web site which claims that this
newer formulation must _not_ be used in pre-2000 vehicles,
such as mine. According to a discussion at
http://tinyurl.com/d9ph3

"Note: Engine oils according to VW standards 503 00, 503 01,
506 00 and 506 01 must not be filled in vehicles up to model
year 2000 (Y). " and "Elsewhere in VW literature it states
using 50300, 50301 oils can cause engine damage in engines
they are not recommended for. ie pre 2001"

Most 0W-40 grade oils these days seem to include VW 503.01.
Google doesn't pull up any confirmation of this claim. Can
anyone cast more light on this, and/or any possible reasons
why it would be so?

In the absence of any further info (despite my continued
looking), I'm going to go with my hunch on this, and assume
that the person I quoted above got it wrong when they concluded
(in a part I didn't quote) that current Mobil 1 0W-40 is
unsuitable for pre-2001 VWs.

I'm getting a clear impression that VW means us to use 502 00
oils in pre-2001 cars, and 503 01 for later models. The quoted
VW warning then means that I should avoid 503 01 oils, but only
if they don't also meet 502 00 (and the Diesel-specific 505 00
as well in my case).

John