Castrol React SRF Racing Brake Fluid 1L

Brake fluid is hygroscopic, meaning it actively absorbs moisture from the atmosphere over time. Because of this, most vehicle manufacturers highly recommend completely flushing and replacing your brake fluid every 2 years (or 24,000 miles), regardless of how often you drive. Leaving old fluid in the system significantly lowers its boiling point and causes internal corrosion in your brake lines and ABS pump.

The “Dry” boiling point refers to the temperature at which brand‑new, fresh brake fluid boils straight out of a sealed bottle (0% water content). The “Wet” boiling point is the temperature at which the fluid boils after it has absorbed approximately 3.7% water from the air (usually after 1 to 2 years of use). The wet boiling point is the most critical safety metric, as it represents how the fluid will perform in real‑world, aged conditions.

DOT 3, DOT 4, and DOT 5.1 are all glycol‑ether based and can technically be mixed in an emergency. However, doing so will immediately degrade the performance (and boiling point) of the higher‑rated fluid. You must never mix DOT 5 fluid (which is silicone‑based) with any other DOT rating, as this will cause severe chemical reactions and catastrophic brake failure. Always top up with the exact specification recommended in your owner’s manual.

The most common symptom of degraded or moisture‑heavy brake fluid is a “spongy” or soft brake pedal that goes closer to the floor than usual. You might also experience “brake fade” (a terrifying loss of stopping power) during heavy braking or driving down steep hills. Visually, healthy brake fluid is nearly clear with a slight yellow tint; if it looks dark brown, murky, or black, it is heavily contaminated and needs an immediate flush.