Often overlooked, brake
fluid should be changed at
or near the 30,000 mile mark

 

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Consider changing brake fluid at 30,000 miles or during brake pad replacement

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.
Sometimes used is DOT 5 fluid which can be recognized by it's purple color. DOT 5 fluids are typically silicone-based. DOT 3 and DOT 4 fluids are polyglycol.
Hydraulic system mineral oil brake fluid [HSMO] is a blend of mineral oil and additives. It is the most rare, the most expensive, and is not compatible with any other fluids.


Difference in fluids:

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 fluid.

Change Brake Fluid:

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.

Boiling point

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.