Due to the extreme
operating temperatures of a high performance brake system,
standard “off-the-shelf” brake fluids are not recommended.
Of critical importance in determining a fluids ability to handle
high temperature applications is the Dry Boiling Point and
compressibility.
The Dry Boiling Point is the temperature
at which a brake fluid will boil in its virgin
non-contaminated state. The highest temperature Dry Boiling
Point available in a DOT 3 fluid is 572° F.
The Wet Boiling Point is the temperature a brake fluid will
boil after it has been fully saturated with moisture. The DOT
3 requirement for wet boiling point is a minimum temperature
of 284° F.
There are many ways for moisture to enter your brake system.
Condensation from regular use, washing the vehicle and
humidity are the most common, with little hope of prevention.
Glycol based DOT 3 & 4 fluids are hygroscopic; they absorb
brake system moisture, and over time the boiling point is
gradually reduced.
Wilwood does not recommend using DOT 5 fluid in any racing
applications. DOT 5 fluid is not hygroscopic, so as moisture
enters the system, it is not absorbed by the fluid, and
results in beads of moisture moving through the brake line,
collecting in the calipers. It is not uncommon to have caliper
temperatures exceed 200° F, and at 212° F, this collected
moisture will boil causing vapor lock and system failure.
Additionally, DOT 5 fluid is highly compressible due to
aeration and foaming under normal braking conditions,
providing a spongy brake feel. DOT 5 fluid is best suited for
show car applications where its anti-corrosion and paint
friendly characteristics are important.
Whenever you add fresh fluid to your existing system (never
mix fluids of different DOT classifications), it immediately
becomes contaminated, lowering the boiling point of the new
fluid. For maximum performance, start with the highest Dry
Boiling Point available (try Wilwood’s Hi-Temp° 570 Racing
Brake Fluid), flush the system completely, and flush it
regularly, especially after severe temperatures have been
experienced.
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