Description:
Brake fluid is a specially formulated liquid used in the
brake hydraulic system. Brake fluid must meet one of three U.S.
Department of Transportation (DOT) specifications. DOT3 and DOT4
are glycol-based fluids, which
absorb water. DOT5 is a silicone-based fluid and does not absorb water.
The main difference is that DOT3 and
DOT4 absorb water, while
DOT5 doesn't. Most cars use DOT 3 fluid
from the factory.
Purpose: Since liquids can't be
compressed, brake fluid transmits force to various parts of the
braking system when you step on the brake pedal. Brake fluid must
also have a high boiling point because of the heat generated during
braking and must not freeze during cold temperatures. DOT 3
and
DOT 4 fluids also
attract small amounts
of water that may collect in the brake
system.
Maintenance Tips/Suggestions: Check the brake fluid level in the master
cylinder reservoir regularly, ideally at every oil change. Most cars
use semi-transparent reservoirs that have level markings to make
fluid monitoring easy. If you need to add fluid, use only the type
of fluid recommended in your car's owner's manual. Do not leave the
cover off the master cylinder any longer than necessary; DOT 3 and
DOT 4 brake fluids attract water. Use extreme care when handling DOT
3 and DOT 4 fluid as it quickly destroys paint if spilled. On cars
with disc brakes, it's normal for the fluid level to gradually drop
as the brakes wear. This fluid fills up the space left by the disc
brake caliper pistons as they move outward with brake wear. However,
if you find that brake
fluid needs to be added frequently, there may be a
leak in the hydraulic system. Have the system inspected as soon
as possible by a qualified service technician. Your owner's manual
may specify
periodic
flushing and filling of the brake hydraulic system, which should not be
overlooked. This is a service best left to professional technicians,
as many cars with ABS have specialized
brake-bleeding procedures. Braking systems with ABS can also generate extremely
high hydraulic pressures, which can be dangerous.
Once again, consult a professional service technician if your car
needs ABS or hydraulic system service. Click here to see
a detailed diagram of the brake
system.
