DOT 4 vs. DOT 5.1 Brake Fluid
The DOT specification for DOT 5.1 brake fluid has a higher minimum dry boiling point/minimum wet boiling point (527°F/347°F) than the DOT 4 spec (446°F/311°F,) but these are just minimum specs. Some DOT 4 fluids exceed DOT 5.1 specs.
DOT 3 and DOT 4 fluids are compatible with DOT 5.1 but are not compatible with silicone-based DOT 5. DOT 5 brake fluid is dyed purple to warn against accidental mixing. All Brembo braking products used by Ducati have natural-rubber base seals that are incompatible with DOT 5 silicone-based brake fluids.
The use of the 5.1 designation is quite confusing.
DOT 5.1 is a lighter viscosity glycol-based fluid that was developed for use in ABS systems that need to cycle on and off quickly. It really has no advantage over the DOT 4 fluid recommended by Ducati. DOT 5.1 fluid can have worse performance after absorbing moisture than some of the better DOT 4 fluids.
For example, (expensive) Castrol SRF (590°F/518°F) is used by Formula One teams, ATE Type 200 and Super Blue Racing (536°F/392°F), and Motul RBF 600 (593°F/421°F). Golden Spectro Supreme DOT 4 (520°F/367°F) comes close.
Compare these numbers to Motul 5.1 (518°F/365°F)
Most of us don't change our brake fluid very often so wet boiling point numbers are more important. On the track, brake fade is the main concern so we change the fluid more often and use a higher dry boiling point fluid. Generally, the higher the dry boiling point, the faster the fluid absorbs moisture from the air, Castrol SRF and the ATE fluids are exceptions.
The clutch hydraulics don't see high temperatures like the brake system does so there's no need to use expensive formulations here. Any DOT 4 fluid will suffice, but remember to change it every 12 to 18 months to remove water accumulation in the fluid.
Last edited by Shazaam; Mar 6th, 2011 at 12:47 pm.