Vehicle Brake Fluids

An Essential Guide to Brake Fluids

You probably know that you have to use the right motor oil for your motorcycle, automobile, or lawnmower, but you also need to use the right synthetic brake fluid. Many brands manufacture the three types of brake fluid, providing a vast number of choices.

Your owner’s manual provides you this vital information, but if you misplaced it, you can check the master cylinder of your vehicle. On the cover of the master cylinder, you will find the manufacturer’s stamp that conveys which Department of Transportation (DOT) brake fluid is appropriate for the vehicle. DOT classifies brake fluids by viscosity and temperature range into three categories – DOT 3, DOT 4, or DOT 5.

Because of the differences in the three, you cannot mix them. The dry boiling point and wet boiling point differs between DOT 3 and 4. The glycol-based DOT 3 boils the quickest. It can absorb some water. Most American and Asian built cars use DOT 3. The also glycol-based DOT 4 boils more slowly and can also absorb some water. It gets used in high-performance vehicles including most racing cars and European built vehicles. DOT 5 uses a silicone-base and does not absorb water. If water gets into the system, it negatively interacts with the silicone. Most military vehicles use DOT 5 brake fluid. Rarely, select vehicles use glycol-based DOT 5.1 brake fluid. Its main difference from DOT 4 is its dry and wet boiling points which are much higher than that of DOT 4. Newer cars often use the lower viscosity brake fluids because these thinner fluids circulate more quickly through the ABS, ESP, and TCS brake systems. This has helped them to develop quicker, more responsive braking capabilities.

Five European manufacturers began using low-viscosity fluids exclusively in the early 2000s. These automakers are:

• Audi models from 2006
• BMW models from 2002
• MINI all models
• Saab all models
• Volkswagen models from 2006

Many manufacturers make these DOT 3, 4, and 5 fluids, including Bel-Ray, Brembo, Gunk, Johnsen's, MAG 1, Motorcraft, and MOTUL.

Flush the system when changing the fluid and do not mix the fluids from two different manufacturers.