preferred brake fluid

The silicone DOT 5 fluids are not all they are cracked up to be;

1. It is very easy to entrap air in the fluid when pouring it making it very tough to impossible to bleed it all out. This results in a spongy pedal.
2. Water will not mix with it so any mositure present in the system seperates out and can boil when the brakes get hot resulting in loss of braking power. Also, the seperated water can cause corrosion to happen faster than in the gycol based fluids. Pistons can actually seeze up quicker than with gycol based fluids when the corrosion occurs in the caliper.
3. Even though it has a higher boiling point it becomes compressible at a temperature lower than DOT 3's boiling point resulting in spongy brakes when hot. Gycol type fluids don't become compressible until their boiling point.
4. Its more viscus and does not work well in ABS brake systems.

If you need the highest boling point DOT fluid then DOT 5.1 is what you want. This is still a gycol based fluid and is completely compatable with DOT 3 and 4.

Racing brake fluids can have a much higher dry (no moisture content) temperature rating but they typically have a lower wet (3% moisture absorbtion) temperature rating. This makes them generally not suitable for street car use where the fluid is not regularly changed.