REFLECTOR: DOT 5 Compatability

[Wayne]

Now I'm even more confused. I just looked at my bottle of NAPA DOT 5 silicone brake fluid. It is amber.
  *DOT 5:* This brake fluid has a silicone base. It is purple in color. It is 
  NOT hygroscopic (meaning it cannot and will not moisture) and has a minimum 
  dry boiling point of 500°F (260°C) and a minimum wet boiling point of 356° 
  (180°C) It is not used in many brake applications, seeing primary duty in 
  weekend, antique, and collector cars that sit for long periods and are never 
  driven far. It does not mix with DOT 3, DOT 4, or DOT 5.1. It will not 
  absorb water and will not damage the paint on a vehicle. It is also 
  compatible with the same rubber formulations as the DOT 3, 4 & 5.1 fluids. 
  The problem with it is that it can easily get air bubbles into the system. 
  The air bubbles are nearly impossible to remove and result in poor system 
  performance and poor pedal feel. Although originally developed in the late 
  1960's by General Electric specifically for racing, it is unsuitable for 
  racing for a variety of reasons. (Scroll to the bottom for the scoop on 
  Silicone) If as little as one drop of water enters the fluid, severe 
  localized corrosion, freezing, or vapor lock may occur. This can happen 
  because water is heavier and not mixable with silicone fluids. It is 
  unsuitable for ABS. 

  *DOT 5.1:* This brake fluid is similar to DOT 4 it has a base comprised 
  primarily of Borate Ester. Often in the range of 70 - 80%. To meet 
  specification, it also will contain other additives. It is clear to amber in 
  color. It is hygroscopic (meaning it absorbs moisture) and has a minimum dry 
  boiling point of 500°F (260°C) and a minimum wet boiling point of 356°F 
  (180°C) minimum. It is almost exclusive to Europe, used in high performance 
  cars. It can be mixed with DOT 3 or DOT 4 without damage to the system. It 
  maintains higher boiling point than DOT 3 or DOT 4 fluids due to its even 
  greater borate ester content. It is excellent for severe duty and racing 
  applications. The problem with it is that it costs more than other fluids 
  and there is limited availability in the USA. It also absorbs moisture out 
  of the air and thereby reduces its boiling point. It can also damage the 
  paint on a vehicle. 

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