Brake fluid is hygroscopic. Hygroscopic is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing substance becoming physically changed somewhat. A new bottle is considered “dry” with a higher boiling point. However, since it’s a hygroscopic fluid it will absorb water over time lowering it’s boiling point to the “wet” level.
When it comes to boiling points for your daily driver the wet boiling point number is more important than dry because the fluid stays in your car for at least two years. After months or years of changing climate conditions (temperature & humidity) the brake fluid performance is closer to the wet boiling point than the dry boiling point.
Once brake fluid soaks up moisture it thickens and will not be able to withstand the heat created under the pressure of heavy braking. What happens next is a significant drop in performance and in the fluids boiling temperature. When the fluid boils it turns some of the brake fluid into vapor and forms air bubbles. The end result is a soft or spongy brake pedal. Another indication of this is there will be significantly more pedal travel.
G-LOC Brakes, LLC does not recommend using a silicone based brake fluid with any of its products. For more information, please scroll down to the bottom of the page to the section labeled “a word of caution.”
| Fluid type | Fluid description | Dry/Wet Boiling Point | Size/per bottle | Price/per bottle |
| Brembo LCF600 | Excellent choice for street and/or track use. Proven low compressibility. It gives a firmer pedal feel then most other brands. | Dry: 316°C (601°F) Wet: 204°C (399°F) |
16.9oz/ .53 quarts .50 Liter/ 500ml |
$20.95 |
| CASTROL SRF | The SRF is the absolute best brake fluid on the market due to its extremely high dry & wet boiling points. If you want the best the Castrol SRF is it. | Dry: 310°C (590°F) Wet: 270°C (518°F) |
1 Liter | $79.95 |
| MOTUL RBF600 | Developed for all forms and levels of racing, the RBF600 is one of the most popular fluid’s on the market today. | Dry: 312°C (594°F) Wet: 216°C (421°F) |
16.9oz/ .53 quarts .50 Liter/ 500ml |
$22.50 |
Brembo LCF600
‘Typical’ New Dry Boiling Point = 316°C (601°F)
‘Wet’ E.R. (Equilibrium Reflux) Boiling Point = 204°C (399°F)
Brembo LCF 600+ exceeds all DOT 4 requirements and is suitable for use in all DOT3, DOT4, and DOT 5.1 brake system applications.
LCF 600+ is an ideal choice for racing or performance use – combining ultra-high dry boiling point, low compressibility, and consistent pedal feel.
IMPORTANT NOTE
DO NOT USE Brembo LCF 600+ fluid in contact with any type of magnesium components (e.g. gearbox / clutch components) as a chemical reaction is caused resulting in gases being generated. This will then prevent the clutch hydraulics from working efficiently.
CASTROL SRF
‘Typical’ New Dry Boiling Point = 310°C (590°F)
‘Wet’ E.R. (Equilibrium Reflux) Boiling Point = 270°C (518°F)
The ultimate racing brake fluid
Castrol SRF Brake Fluid’s unique silicon ester technology absorbs less water than conventional glycol ether fluids and prevents the fluid’s high temperature performance from deteriorating. Its wet boiling point of 270°C is vastly superior to the minimum requirement of 155°C demanded by the current US DOT 4 specification. Its ability to withstand temperatures in excess of 300°C and superior resistance to the effects of absorbed water have established Castrol SRF Brake Fluid as the world’s premier fluid for the hydraulic brakes used in all forms of motorsport and racing.
MOTUL RBF600
‘Typical’ New Dry Boiling Point = 312°C (594°F)
‘Wet’ E.R. (Equilibrium Reflux) Boiling Point = 216°C (421°F)
Motul RBF 600 is a 100% synthetic fluid for hydraulic-actuated brake and clutch systems. Specifically designed to resist the high temperatures of actuated (steel or carbon) racing brakes and clutch systems.
Motul RBF 600 far exceeds the standards of DOT 3 and DOT 4.
The RBF 600 container is filled with Nitrogen to increase shelf life and eliminate contamination while factory sealed.
Extremely high dry and wet boiling points help prevent vapor lock and brake fade during hard use.
SILICONE BRAKE FLUIDS – A WORD OF CAUTION
G-Loc™ Performance Brakes markets silicone brake fluids nor recommends their use with any braking system.
Virtually all of the problems with silicone brake fluids reflect certain properties of silicone fluids identified by us over many years and recently ratified in SAE publications, specifically: high ambient viscosity; high air absorption; high compressibility; low lubricity; and immiscibility with water. Research has shown that these properties of silicone fluid result three performance problems:
Long Pedal Travel or “Spongy” Pedal caused by:
- High compressibility, up to three times that of glycol based fluids;
- High viscosity, twice that of glycol based fluids, leading to slow rates of fill and retention of free air entrapped during filling, and hence bleeding difficulties.
A Sudden Loss of Braking resulting from:
- Air absorption – gasification of absorbed air at relatively low temperature produces vapor lock effect;
- Immiscibility (failure to mix) with water – whilst the presence of dissolved water will reduce the boiling point of glycol based fluids, any free water in silicone-filled systems will boil and produce vapor lock at much lower temperatures (100°C or thereabouts)
“Hanging On” of brakes due to:
- Low lubricity – in disc brake systems the sole mechanism for normalization of system pressure upon release of pedal pressure is a designed-in tendency of seals to recover to their ‘at rest’ attitude. Low lubricity works against this tendency.
- High viscosity exacerbates the effects of low lubricity. The high price of silicone fluids does not produce higher performance in hard driving or even normal road use.
Bleeding Your Brakes
When you bleed the brakes this is the procedure for releasing any air or moisture trapped in your brake fluid system. Flushing or changing your brake fluid consists of flushing the old brake fluid out of the master cylinder, brake lines, and calipers while replacing it with fresh fluid. When bleeding your brakes, always start with the caliper farthest from the master cylinder. If you are going to use a mechanical/power bleeder, then following the instructions that came with your mechanical/power bleeder (and consult with a professional). If you choose to bleed your brakes manually then it will take two people do complete this task properly. Have one person operating the bleed screw while another person slowly and repeatedly depresses the brake pedal. Make sure you CLOSE the bleed screw before the brake pedal is released. Always remember to NEVER reuse old brake fluid. Please discard of any and all used brake fluid responsibly. G-LOC Brakes, LLC™ recommends consulting with a properly trained technician before bleeding your brakes
Why bleed or flush your brakes?
To remove moisture, air, atmospheric dirt, and abrasive metal wear particles from moving parts in the master cylinder and calipers that have entered the system. Brake fluid needs to be replaced periodically because brake fluid will absorb moisture over time which can lower the boiling point enough to make it boil at very low temperatures. Moisture is very compressible which will give you a soft (spongy) pedal. This will occur whether a vehicle has been driven 50,000 miles over the course of a year, or if the vehicle has been sitting in your garage for a year. Brake fluid contamination is a function of time and humidity, and has nothing to do with the mileage driven or not driven. Moisture can enter the brake system through seals, connection points, calipers, the master cylinder reservoir, and through microscopic pores in the hoses. Please note that moisture can enter your brake fluid system every time the fluid reservoir is opened. Please try to not open your brake fluid reservoir unnecessarily.
Vehicles with antilock braking systems (ABS) are even less tolerant of contaminated fluid and air than non-ABS vehicles. The ABS hydraulic pump operates at several thousand psi, forcing brake fluid through very small valves. This can whip air and brake fluid into something like the foam on a latte. This can make bleeding extremely difficult for an individual to do without the proper equipment. Those same valves and pump can be damaged by these tiny abrasive particles.
Air that has entered the ABS controller can be bled out but most likely requires the use of an expensive (and sometimes proprietary) ABS scan tool to cycle the pump and valves to purge the last of the air and foam. G-LOCBrakes, LLC recommends consulting with a properly trained technician before bleeding your brakes.