Can DOT 5 Brake Fluid Be Used Instead of DOT 3 or DOT 4?
Always refer to vehicle owner's manual for what the manufacturer
recommends or warns against. As a rule, vehicles equipped with
anti-lock brakes (ABS) should not use DOT 5 brake fluid.
DOT 5 brake fluid is silicone based. DOT 3 (standard) and DOT 4
(heavy-duty) are glycol-based. It can be distinguished from
conventional brake fluids by its purple color (which comes from a
dye).
Silicone does not absorb moisture. DOT 5 brake fluid does not become
contaminated with moisture over time as conventional DOT 3 and 4
brake fluids do. Silicone is also chemically inert, nontoxic and
won't damage paint like conventional brake fluid. It also has a
higher boiling point.
Because of this, it is often marketed as a premium "lifetime" brake
fluid. It is often used to preserve brake systems in antique
vehicles and those that sit for long periods of time between use.
DOT 5 silicone brake fluid is also very expensive (costing four to
five times as much as ordinary brake fluid), and it won't mix with
glyco- based brake fluid (creating concern over sludging if all old
fluid isn't removed when a system is refilled with silicone).
Silicone also has slightly different physical properties and
compressibility, making it unsuitable for ABS systems calibrated to
work with DOT 3 or 4 brake fluid.
