How to choose Brake Fluid
Brake fluid is a hydraulic fluid used in your brake lines. It takes the force your foot exerts onto the brake pedal and transfers it into braking pressure that then clamps your brake rotors
, effectively slowing your car down. We use brake fluid due to it's hygroscopic nature and it's ability to resist compression. Essentially, you transmit all your force from the pedal to the brake rotor
without losing energy due to fluid compression.
Now, because the brake rotors
and brake calipers exert a high amount of heat, brake fluid must have a high heat tolerance. Otherwise, it would simply vaporize inside your brake lines and negate the purpose of the brake fluid. This is dangerous and results in your brake system not functioning properly.
Boiling Point is the maximum temperature before your fluid starts to boil. To further complicate things, there is a Dry Boiling Point and a Wet Boiling Point. Wet simply means the boiling point of a fluid after it has absorbed a certain percentage of moisture* (remember, it's hygroscopic). Dry is fresh fluid from a canister that hasn't been opened.
Below, we have the quality standards for each of the fluid classes.
- DOT 3 205 C/401 F (Dry) 140 C/284 F (Wet)
- DOT 4 230 C/446 F (Dry) 155 C/311 F (Wet)
- DOT 5** 260 C/500 F (Dry) 180 C/356 F (Wet)
- DOT 5.1 270 C/518 F (Dry) 190 C/374 F (Wet)
It's always recommended to only stick with the DOT rating your car recommends.
Using a DOT rating other than what is recommended may cause improper brake operation or premature failure.
*Wet boiling point is defined as 3.7% water by volume.
**DOT 5 is a synthetic non-hygroscopic fluid and should only be used for designated cars that support DOT 5.