In a message dated 96-06-21 17:03:04 EDT, chrisp@dsinet.dgtl.com (Christian
Pittack) writes:

<< I was at Costco the other day and saw a case of Chevron Delco Motor Oil.
 The
 carton said specially formulated for Diesel Engines for use with all
 fuels...even low sulfer ones!  What the heck does these mean?  Is this oil
 different than others, if so how?  It had all the standard API ratings
 including CD (is that the Diesel one?).  With all the recent discussion on
 oils, maybe someone can clue us in!
  >>
Diesels do require different additive packages than Gas engines.  The biggest
difference is the oils ability to neutralize acid.  All Diesel fuels contain
some sulfur.  When the sulfur gets in the oil, it reacts with moisture to
form Sulfuric Acid.  The oils ability to reduce this acid is known as the TBN,
( total Base Number).  The higher, the better.  Oils acceptable for use in
diesels are rated in "C" designations.  VW's and most diesel cars and trucks
require at least CC or CD.  Real trucks use ratings much higher such as CD=IV
or CF etc.  Note that the last case of Castrol 20-50 I purchased had no
Diesel ratings at all.  This leads me to believe it should not be used at all
in diesels.  Even the blurb on the label no longer mentions diesels.  I use
the Castrol Super fleet in diesels.  It is a 15-40 and has all those higher
diesel ratings.  It is also an excelent gas engine oil and for milder
climates, an ideal compromise between 10-40 and 20-50.  I use it in diesels
all year in New York.  

Dennis.