According to the guys at the VW dealer Vanagon's must use the blue Autobahn
coolant because it contains silicates.  Your claim that silicates are an
abrasive is not entirely true, talc is a common silicate and is a lubricant,
see < http://www.britannica.com/bcom/eb/article/2/0,5716,72882+1,00.html >.
On the other hand "silicates make up about 95 percent of the Earth's crust
and upper mantle" <
http://www.britannica.com/bcom/eb/article/9/0,5716,69519+1,00.html >
including many abrasives.  I would say that it is not possible to determine
the use of silicates in Autobahn coolant from this information, silicate is
just too general a term.

I would however say that if VW sold new Vanagon's with silicate in the
coolant, and VW continues to sell Autobahn coolant with silicates along with
the silicate free formula I am going to use the blue Autobahn w/ silicates.

One other possibility  is that these "long life" coolants contain other
lubricants that make up for the lack of silicate, but this would be assuming
that the silicates in the blue Autobahn are lubricants.

dave
dave@251.org