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Hi,
There's a lot of misinformation about Brake Fluid floating around out there. All Brake Fluid is Hygroscopic, except DOT 5 (which is Silicone Fluid - Race Application only), meaning that it readily absorbs moisture from the air.
All Brake systems are vented at the Reservoir (or you'd create a vacuum and no fluid would be supplied to the system from the Reservoir). Normal Humidity, especially on rainy days, and believe it or not, when you wash your car is where this moisture comes from.
You do not want to use DOT 5 (Silicone), because unlike DOT 1, 2, 3 and 4 which mix with water, the Silicone won't.
Water is heavier than Brake Fluid and if DOT 5 is used, all the water will migrate to the lowest point in the system - the Calipers where it will readily boil as well as corrode the Piston/Bore, better to have the water in solution as it isn't so highly concentrated in the Caliper. Dot 5 has the highest Dry Boiling Point which is why it's used in Racing - they swap fluid every race. It was initially spec'd for the US Military because it had good sub-freezing performance, but due to the accelerated wear to the Brake components and consequent expense, the Military has dropped this specification and reverted back to Polyglycol-based fluid - DOT 4.
ATE Super Blue Fluid and ATE Gold (properly known as Typ 200) are exactly the same Fluid - same Dry Boiling Point, same Wet Boiling Point. The only difference is the color to make flushing the system easier because of the Visual check available to know that the entire system has been flushed - look for the color change in the Catch Bottle. So, you should alternate between Super Blue and Typ 200 (Gold) every Fluid change.
Your Mechanic and AX Instructor are incorrect. Don't believe me? Look at the attached picture of a Can of each and compare their labels. Hope this helps...
Happy Motoring!... Jim'99
Last edited by MNBoxster; 04-17-2007 at 07:45 AM.
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