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Boiling Points
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 3 brake fluid is no less than 205°C (401°F),
and the minimum wet ERBP is 140°C (284°F). That
might not seem very high, but in most brake systems
the fluid in the caliper won’t reach that
temperature unless the brakes are abused. It only
takes four percent water contamination to bring a
DOT 3 fluid’s boiling point down to the federal
limit.
AMSOIL
Series 500 High-Performance DOT 3 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 500 High-Performance DOT
3 Brake Fluid's superirior 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).
Compressibility
When a fluid is non-compressible it means it won’t
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 500 High-Performance
DOT 3 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 there’s 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 won’t
discover the reduced braking ability until it’s too
late.
Many owner’s 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.
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