---- David Beierl <dbeierl@ATTGLOBAL.NET> wrote:
> At 12:07 PM 8/19/2010, Luke Bakken wrote:
> >The brake fluid reservoir on my '89 syncro specifies DOT 4. Can't
> >speak for prior years.
>
> '89 manual says 3 or 4, reservoir says 4.
>
> Regardless, DOT 5 is totally forbidden.  It's completely different
> and incompatible.
>
> I believe it's safe to say that 4 may be used in any application
> where 3 is specified.
>
> Yours,
> David

David, 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.  If DOT 4 fluid could always replace DOT 3, why wouldn't the manufacturers just drop the DOT 3?

BTW, my 2006 Prius specifies DOT 3, as does my neighbor's 2010, and both owner's books state that damage to brake system components may occur if the wrong fluid is used.  My '91 Volkswagen Vanagon GL Campmobile is not here right now, and took the owner's book with it, but I'll check later to see what if anything the book states, beyond specifying a fluid.

DMc

--
David McNeely