Castrol SRF Synthetic Racing Brake Fluid

Silicone-based fluid repels water, creating extremely high boiling points

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  • Dry Boiling Point = 312° C (594° F)
  • Wet Boiling Point = 270° C (518° F)
  • "DOT4" (exceeds DOT5 boiling points)
  • Normal viscosity
  • 1 liter bottle
Castrol SRF Synthetic Racing Brake Fluid is an exceptional high-performance brake fluid specifically developed for the extreme braking conditions found in motorsports applications. SRF is a hydrophobic fluid - it repels water instead of absorbing it. This allows it to maintain a very high wet boiling point compared to hygroscopic fluids.

All conventional brake fluids are hygroscopic - they absorb water. Water finds its way into the braking system a number of ways. Not only will it lead to rust of critical components but it will decrease the effectiveness of brake fluid. The water will boil sooner than fresh brake fluid and the water vapor is what results in a spongy brake pedal. Water also compresses easier than brake fluid, contributing to a soft pedal. The hydrophobic silicone mixture in SRF makes it virtually immune from the effects of water. This makes SRF the superior choice for racers as the boiling points of the SRF stay extremely high. There are some drawbacks to be aware of: service, compatibility, and cost. Because water is not easily absorbed, it still must be drained or pumped out of the system. Water that does boil creates a gas that can clog the system. So more frequent brake flushes are required. SRF is also not very compatible with other types of brake fluids without its performance degrading substantially. Old fluid must be completely drained from the system and multiple flushes with SRF are recommended. This makes SRF quite pricey compared to other fluids but the performance is unequaled.

Because it is a brake fluid intended for racing, it does not have to meet DOT requirements. However, testing has shown that it would be classified as a DOT4 fluid.

BMW Fitments:

F22 / F23 (2014+) > M235i-Racing
F22 / F23 (2014+) > M240i-Racing
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