As the brake system heats up, brake fluids with
low boiling points begin to vaporize. The brake pedal must travel
further to apply the same amount of force on the brakes, causing
a spongy feeling. If enough of the brake fluid vaporizes, brake
system failure may occur. Brake fluid boiling points are measured
on two separate scales:
Dry equilibrium reflux boiling point (ERBP)
- the boiling point of new, freshly-opened, unused fluid.
Wet ERBP - the boiling point of a brake
fluid after it has absorbed three percent water.
The minimum dry ERBP for DOT 4 brake fluid is
230°C (446°F), while the minimum wet ERBP is 155°C
(311°F). Their higher boiling points make DOT 4 fluids appropriate
for high-performance cars and motorcycles and for vehicles used
for towing or in mountainous regions.
AMSOIL Series 600 DOT 4 Racing Brake Fluid is
formulated with the best zinc-based anti-corrosion additives and
pH stabilizers. It is designed for high-temperature stability,
yet flows easily at low temperatures. AMSOIL Series 600 Racing
Brake Fluid's superior additive package provides good lubrication
throughout the system and can raise boiling points to more than
232°C (450°F). It keeps water in suspension, slowing its
effects on the brake system. AMSOIL Brake Fluids have high boiling
temperatures, ensuring maximum life and reliable braking power,
even in extreme conditions. AMSOIL Series 500 High- Performance
DOT 3 Brake Fluid has a dry ERBP of 274°C (525°F) and
wet ERBP of 156°C (313°F). AMSOIL Series 600 DOT 4 Racing
Brake Fluid has a dry ERBP of 304°C (580°F) and wet ERBP
of 210°C (410°F).
When a fluid is non-compressible it means it
wont compress into a smaller volume when pressure is applied.
In a brake system, fluid pressure is multiplied by the master
cylinder and can reach more than 1,000 pounds per square inch
(psi) in the lines. Like any other hydraulic fluid, brake fluid
must be non-compressible at the expected pressures to transmit
force from one end of the system to the other while simultaneously
lubricating the pistons and rubber parts as they move through
their bores. If the fluid were to compress, all braking power
would be lost. AMSOIL Series 600 DOT 4 Racing Brake Fluid remains
non-compressible, even at the highest pressures generated in automotive
brake systems. AMSOIL Brake Fluid provides superior stopping ability
under the most demanding conditions.
Brake Fluid Maintenance
Brake fluids fail either because they boil or
because they cease to provide adequate lubrication and corrosion
protection. Both reasons for failure are the result of contamination,
usually by water or petroleum products.
DOT 3 and DOT 4 polyglycol ether-based brake
fluids are hygroscopic, which means they absorb water easily and
hold it in suspension, similar to antifreeze. In most climates,
moisture seeps into the brake system continuously through the
various seals and microscopic pores of the flexible brake lines.
This seepage can accelerate as a vehicle ages and theres
almost no limit to how much water the fluid can absorb. By the
time brake fluid has been in the system for three years, it can
easily reach its wet boiling point. Because this happens gradually,
most drivers wont discover the reduced braking ability until
its too late.
Many owners manuals recommend changing
brake fluid every 24 months to remove moisture. Approximately
half of all cars and light trucks in the U.S. over 10 years old
have never had the brake fluid changed. In addition, powersports
applications such as motorcycles, ATVs and UTVs require routine
brake fluid changes as well.