[SEL] OT. Brake fluids

[Rob Skinner]

Hi, Curt.  This is a subject over which I spend an abnormal amount of  
time pondering.  In a nutshell, you can mix DOT 3, DOT 4, and DOT 5.1  
without adverse effects to the system.  They are all glycol based.

DOT 5.0 is silicone based, and you can not mix it with the others.   
5.1 is several times more compressible than glycol based fluids and  
can allow a spongy feel.

Eash spec contains a bunch of criteria, but he one of concern to most  
people is boiling point.  The higher DOT specs have higher minimum  
boiling points.  As you probably know, when your fluid boils, your  
pedal goes to the floor and it gets weird very quickly.  Glycol based  
fluids are hygroscopic.  As the fluid absorbs water, the boiling point  
plummets.  The fluid even absorbs water as it sits on the shelf, so  
the recommended shelf life is two years.

So, to answer your question, I don't think your sister will have a  
problem, unless she races her Volkswagon or uses it for hauling heavy  
loads down steep hills.  She's probably better off that the guys went  
out and bought a new jug of fluid, rather than using a bottle that's  
been sitting on the shelf for several years.

As a side note, I'm skeptical for the need for Castrol in European  
cars.  More than likely, it's a rumor that was started by an  
overzealous Castrol salesman, or by a manufacturer who recomended  
Castrol in it's owner's manual.


	
Rob Skinner
Antique Stationary Engines
La Habra, California

rob at rustyiron.com
www.rustyiron.com





On May 18, 2009, at 2:15 PM, curt at rustyiron.com wrote:

> Years ago one had to be careful when servicing foreign cars about
> computability with brake fluids. I'm not speaking of the silicone  
> brake
> fluid, but rather the regular (glycol?) brake fluids. Seems like most
> European cars used Castrol brake fluid and I was taught to only use
> Castrol brake fluid in these cars, lest the rubber parts soften and  
> lead
> to brake failure.
> Is this still the case?
>
> I found nothing about this on a quick Internet search, so maybe the  
> issue
> has been resolved.
>
> My sister has a newer VW and they added brake fluid (not Castrol) they
> bought at a local auto parts store. Just wanted to make sure she  
> doesn't
> have an issue later.
> Curt Holland