Issue link: http://digital.nexsitepublishing.com/i/108533
thetic brake fluids that exceeded the DOT 5 minimums. These syn‑ thetics, unlike the silicones, are based on a mixture of glycol ethers and borate esters that are completely compatible with conventional fluids, but still retain some degree of moisture absorption that varies depending upon composition. DOT refers to them as DOT 5.1 brake fluids. These high performance fluids first started showing up in the U.S. in racing applications in the 1992/1993 time period, and caught on quickly with the sports car people. Motul, a French manufacturer, has been a supplier of this type of high performance brake fluid. The first Motul 300C racing brake fluid was rated as a DOT 3 fluid because even though it had a very high 575F dry boiling point, it was very hygroscopic and could only meet the DOT 3 wet specification. The currently available Motul brake fluids now include two more recently developed fluids, Motul 600 and 660. The Motul 600 has a dry boiling point of 595F and the 660's dry boiling point is 617F, but has a greater decline with water absorption than the 600.. Figure 2 presents curves of brake fluid boiling point temperature as a function of percentage water absorption. Curves are shown for four fluids; Motul 660 Racing and Motul 600 Racing, Porsche DOT 4‑200 (the latest factory fluid), and Castrol GTLMA DOT 4, a widely available conventional fluid. The Porsche DOT 4‑200 fluid, developed in conjunction with ATE in 1992, is now installed in all production Porsches at the factory and is available in one‑liter quantities from the dealers. It has also been available commercially as ATE 200 This fluid has a dry boiling point of 545F and a wet boiling point of 392F, which represent major improvements over the previously available Figure 2. Effect of Water Absorption on Brake Fluid Boiling Point DOT 4 fluids as well as DOT 5 specs. A product similar to the Porsche fluid (if not the same) is ATE Type 200 brake fluid, which is also available. www.pnwr.org June 2011 37