Understanding Brake fluid
DOT 3 DOT 4 and DOT 5.1 are Glycol based brake fluids whereas DOT 5
are Silicone based... Glycol based fluids are designed to signal
moisture contamination by changing color... the fluid will start to
turn golden, then light brown, then dark brown indicating that it has
absorbed progressively more moisture. Eventually, if left unchanged
beyond the recommended service interval, the fluid will become dark
and yukky, indicating high amounts of water absorption and thus badly
contaminated fluid... user friendly Glycol based fluids also reduce
the effect of both corrosion and compressibility because it is not
only designed to accept significant amounts of moisture, but even to
neutralize it by dispersing this moisture evenly throughout the
system, thus preventing its concentration in any one area...
Boiling point of Glycol based brake fluids
DOT 3 205 °C (401 °F)
DOT 4 230 °C (446 °F)
DOT 5.1 270 °C (518 °F)
DOT 5 Silicone based fluid will not turn color to signal moisture
content...
Boiling point of Silicone based brake fluids
DOT 5 260 °C (500 °F)
If you wish to use the latest in Glycol base fluids then its DOT 5.1
Note: DOT 5 silicone was created at the request of the military for
use in vehicles that are required to be parked for years at a time and
be ready for deployment. Harley-Davidson used DOT 5 until a decade ago
because it would not negatively affect paint but currently specifies
DOT 4 or 5.1
WARNING: Dot 5.1 glycol (yellow) and Dot 5 silicone (purple) will not mix.
Boiling points
Moisture Contaminated Glycol fluids...
Dot 5 versus Dot 5.1 they do not mix...
Motul 5.1