dot 4 specification

[Curtis_Valk]

For anyone who ever wondered what the difference between dot 3 and dot 4 brake fluid is here are two spec charts for comparison:  http://www.miswa.com/dot3.html
http://www.miswa.com/dot4.html

This discussion originated at Greg's wrench session in Seagoville yesterday.  It looks like the only difference in spec is boiling point (dot 4 is higher of course) and extreme cold viscosity (dot 3 has a slight edge, that makes sense).  All other critera in the spec are identical according to these charts.

Of course, the advertizer who published these charts does so to show that their product EXCEEDS dot standards for both varieties, so the dot standards like just about any other standard is the minimum acceptible standard for that category.

If anyone else has additional info on this subject, please contribute.  Ignorance is NOT bliss, if I don't know something I WANT to know that I don't know (if you know what I mean).

Curtis

[Curtis_Valk]

Also, in this blurb http://www.dnd-automotive.com/chassis/brake-fluid.htm I learned that dot 3 and 4 are both glycol based while the non-compatible dot 5 is silicone based and will not absorb moisture over time.  Interesting, huh?

Curtis

P.S.  Another good article:  http://www.xs11.com/tips/maintenance/maint1.shtml

[Marc Albea]

Here's another interesting article on Brake fluids

http://www.stoptech.com/whitepapers/brakefluid1a.htm