Often overlooked, brake
Types of Brake fluid
The most popular brake fluids used in
today's cars are DOT
3 and DOT 4, both of which are clear to amber in color.
DOT 3 and DOT 4 have an affinity for moisture
causing both the reduction of the boiling point and also
rust and corrosion problems in the brake system. Dot 5 fluid can withstand
very high temperatures and has no affinity to moisture. However, it is higher in price and
it's air retention properties make it difficult to bleed air from the brake system. It
is not used in cars equipped with ABS because of this. HSMO has the
highest boiling point, and it does not contribute to rust or corrosion. HSMO
can be idenified by it's green color. No other fluid can be used in cars
equipped with this
Many drivers overlook this critical fluid, believing that if the car stops, the brake system is operating properly. In our shop we recommend the fluid be changed each 30,000 miles or sooner if the fluid has a dark color; which seems to indicate the presence of moisture.
Brake fluid is subjected to very high temperatures, especially in the wheel cylinders of drum brakes and disk brake calipers. It must have a high boiling point to avoid vaporizing in the lines. This vaporization is a problem because vapor is compressible and negates hydraulic fluid transfer of braking force. Stop and go driving, mountain driving and "riding" the brakes will cause brake temperatures of several hundred degrees.