fwiw, my 85 vanagon owner's manual says 'Dot 4 or Dot 3' brake fluid ..
and I would expect those to be compatible with each other.

they are very specific about not using other types of brake fluid such as
silicone BF,
since that's not compatible at all with conventional Dot 3 or 4 brake fluid.

----- Original Message -----
From: "Dave Mcneely" <mcneely4@COX.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 19, 2010 5:29 PM
Subject: Re: brake question

Michael, what do you want me to document -- that there are differences in
chemistry?  From whence do differences in boiling point arise?  David has
already stated that Chevron considers DOT 4 to be a replacement for 3.  I
know that owner's manuals I have specify one, not the other.  I'll see what
I can find stating that there are chemicals in one that are not in the
other.  DMc

---- Michael Snow <slowmachine82@GMAIL.COM> wrote:
> On Thu, Aug 19, 2010 at 4:21 PM, Dave Mcneely <mcneely4@cox.net> wrote:
>
> >I may be wrong (never happened before ;-) ), but I think there are some
> >incompatibilities in >materials, such that chemical interaction, or lube
> >problems may occur whenever 4 is >substituted where 3 is specified or
> >vice versa. There are some differences in chemistry, >hence the different
> >names.
>
> Please cite any credible source (brake fluid manufacturer, DOT
> standard, etc.) to support this assertion.  This will live forever in
> the list archives and create confusion where there should be none.
>
> --
> Michael Snow
> 1987 Syncro TiiCo
> 1982 Westfalia 1.9TD
> http://slowmachine82.blogspot.com/

--
David McNeely