The Stovebolt Site Forums The Shop Area Driveline Dot 3 to Dot 5 Brake Fluid

Kevin, that is indeed an interesting read and reveals very confusing terminology. One would think a new glycol based fluid should be named 4.1, rather than 5.1 which suggests it is silicone based. To add to the comment about silicone being lighter than water I would like to relate my only experience with DOT 5. I know that members of this site have used DOT 5 successfully but here goes anyway. A neighbor began working on a 70s RV he purchased and he borrowed some of my tools to go through the brake system. The previous owner had converted the brake fluid to DOT 5. When he disassembled the wheel cylinders they all had water and horrible rust pooled at the lower dependent portions of the cylinders, requiring replacement. This vehicle had sat outdoors for several years unused. But this outdoors was Phoenix, AZ. I don't know how that much water got in there, whether it had been driven through water or whether our winters are moist enough to promote condensation in the cylinders. I don't know whether it would have been worse with conventional brake fluid or not. I came away thinking that I would stick with glycol based fluid and just bleed the brakes once in a while to remove any moisture.