Posted by John Waak on Monday, April 12, 2004 at 11:05PM :
In Reply to: DOT 3, 4, or 5? posted by J Gilly on Monday, April 12, 2004 at 7:41PM :
Brake fluids are really getting confusing. Some DOT 4, and most DOT 5 fluids are silicone based. One advantage of silicone is that it wont absorb moisture. If the fluid is not silicone, it is in all probability glycol based. Whichever fluid type you use, be sure you don’t mix glycol and silicone, or as a general rule any DOT 3 or 4 with a DOT 5. If they are mixed, you can look forward to gelling and starting your brake work all over again. Since you are starting with a clean system, this should not be a problem. Although, even with a clean system you may want to flush the system with alcohol before adding your fluid. DOT 5 has the added advantage that it won’t harm painted surfaces. A disadvantage of DOT 5 is that it is rather thick, and pouring it into the system without getting air bubbles trapped in the system is tricky. DOT 5 is used in racing applications where high temperatures can boil away DOT 3 or 4. I believe DOT 5 has a typical 500+ degree boiling point as compared with 450 degrees for DOT 4, and 400 degrees for DOT3. Although DOT 4 and 5 are less absorbent than a glycol DOT 3, moisture still enters the brake system through condensation and humidity. Moisture that is not absorbed by the brake fluid will bead and settle in low points in the system. And where the moisture collects, there will be the potential for rust regardless of the type fluid you are using. I personally see little value in DOT 5 for a Power Wagon. A good DOT 3, and a yearly bleeding is hard to beat. But if you want a superb DOT 3/4, two good brands are Castrol LMA (Low Moisture Activity), and ATE Super Blue Racing and ATE TYP 200. The latter is recommended by BMW for use in their vehicles. The ATE is very slow moisture absorbing, comes in a metal can (plastic lets humidity in), and has a higher wet boiling point than the Castrol, so you can maybe stretch that brake-bleeding job out for a few years.
Good luck!
http://www.castrolusa.com/products/productpage.asp?product_id=14&product_category=3
http://www.machv.com/atesublrabrf.html
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