AMSOIL High Performance Synthetic Brake Fluids
DOT 3 and DOT 4

What is Brake Fluid?

Brake fluid is a type of hydraulic fluid. It is used to transfer force under pressure from where it is created through hydraulic lines to the braking mechanism near the wheels. Braking applications produce a lot of heat, so brake fluid must have a high boiling point to remain effective and must also not freeze under normal temperatures.

Cause of Brake Fluid Failure

Brake fluids fail either because they boil or because they cease to provide adequate lubrication and corrosion protection. Both reasons for failure are the result of contamination, usually by water or petroleum products.

Water contaminates the brake system by seeping through microscopic pores in flexible brake lines and seals and through the reservoir fill cap when opened. Once inside, it quickly works to corrode brake parts, lines and seals, leading to eventual system failure. DOT 3 and DOT 4 polyglycol ether-based brake fluids are hygroscopic, which means they absorb water easily and hold it in suspension, similar to antifreeze, slowing its corroding affects on the brake system. Water seepage can accelerate as a vehicle ages and there's no limit to how much water brake fluid can absorb.

Water lowers the boiling point of brake fluid, which will eventually lead to failure. After two years of service, the average boiling point of brake fluid will have dropped below the minimum federal requirements. Because this happens gradually, most drivers won't discover the reduced braking ability until it's too late.

Brake Fluid Boiling Points Determine Protection and Reliability

The extreme pressure and high heat common to braking can push conventional brake fluids beyond their boiling points, causing them to vaporize, or "boil-off." The brake pedal must travel further to apply the same amount of force on the brakes, causing spongy brakes. If enough of the brake fluid vaporizes, brake system failure may occur. Even more problematic, water contamination can drop the boiling point of conventional fluids below safe standards, accelerating the rate at which they boil off.

Brake fluid boiling points are measured on two separate equilibrium reflux boiling point (ERBP) scales:

• Dry ERBP - the boiling point of new, freshly-opened, unused fluid
• Wet ERBP - the boiling point of a brake fluid after it has absorbed three percent water

The Department of Transportation (DOT) has set minimum standard requirements (shown in the charts below) to ensure brake fluids will provide adequate protection.

Note: Because brake fluids are hygroscopic, the wet boiling point is of much greater concern than the dry boiling point.

AMSOIL DOT 3 and DOT 4 Brake Fluids Far Exceed DOT Minimum Standard Boiling Points

The unique chemistry behind AMSOIL Synthetic Brake Fluids push their boiling point temperatures well above Department of Transportation (DOT) minimum standards even when contaminated with 3 percent water, as shown in the charts below. AMSOIL Brake Fluids feature high wet boiling points for maximum life, superior performance and reliable braking, even in extreme conditions. These products have one of the industry's highest boiling points available.

*Dry equilibrium reflux boiling point (ERBP) — the boiling point of new, freshly opened brake fluid.

**Wet equilibrium reflux boiling point (ERBP) — the boiling point of brake fluid having absorbed 3 percent water. Only 3 percent water contamination is often sufficient to reduce a DOT 3 fluid's boiling point below the DOT minimum.

Superior Additive Package

Brake fluids must protect the metals used in braking systems, such as calipers and master cylinders, from corrosion as moisture enters the system. AMSOIL Synthetic Brake Fluids are formulated with the best zinc-based anti-corrosion additives and pH stabilizers. They provide good lubrication through the system and their superior additive package raises boiling points well above DOT minimum standards.

AMSOIL Synthetic Brake Fluids maintain a stable viscosity over a wide temperature range. They are designed for high-temperature stability and flow easily at low temperatures. Their superior formulation lubricates and protects intricate braking components despite the inevitable water absorption associated with braking systems, delivering longer-lasting performance compared to conventional fluids.

Non-Compressible Even at High Pressures

When a fluid is non-compressible it means it won't compress into a smaller volume when pressure is applied. In a brake system, fluid pressure is multiplied by the master cylinder and can reach more than 1,000 pounds per square inch (psi) in the lines. Like any other hydraulic fluid, brake fluid must be non-compressible at the expected pressures to transmit force from one end of the system to the other while simultaneously lubricating the pistons and rubber parts as they move through their bores. If the fluid were to compress, all braking power would be lost. AMSOIL Synthetic Brake Fluids remain non-compressible, even at the highest pressures generated in today's automotive brake systems to deliver consistent, safe braking.

Ideal Brake Fluid for Racing, Heavy Hauling, Motorcycles and ATVs

The aggressive driving conditions and sudden stops common to some on- and off-road motorcycle and ATV applications can literally boil conventional brake fluid, leaving behind a discolored, dirty solution that can promote deposit formation and corrosion on braking components. Worn brake fluid also fails to deliver adequate protection against water ingress common to powersports equipment exposed to the elements. The synthetic base stocks and superior additives in AMSOIL Synthetic Brake Fluids excel in demanding powersports applications, providing reliable brake lever and pedal response, corrosion protection and longevity as compared to conventional brake fluids. AMSOIL Series 600 DOT 4 Synthetic Racing Brake Fluid features a wet equilibrium reflux boiling point (Wet ERBP) nearly 100°F higher than the DOT minimum, making it the ideal choice for high-performance cars, racing, motorcycles and vehicles used for towing.

How Often Should You Change Brake Fluid?

Brake fluid is vital to safe driving, yet one of the most neglected fluids in vehicles today. Once installed, moisture seeps into the fluid through brake lines and seals, therefore the fluid will need to be replaced when the water content becomes too high. Also, the brake fluid's corrosion inhibitors degrade over time and need to be replaced.

Experts recommend changing brake fluid every 12 to 24 months as preventative maintenance, even more often in wet and extremely humid climates. Many owner's manuals recommend changing brake fluid every 24 months to remove moisture, ensuring reliability and safety. Many European countries require regular brake fluid inspections — half of all cars fail.

In the United States, half of all cars and light trucks that are 10 or more years old have never had their brake fluid changed. In addition, power sports applications such as motorcycles, ATVs and utility vehicles (UTVs) require routine brake fluid changes as well. After only a year of service, brake fluid in the average vehicle may contain as much as two percent water, and up to three percent after 18 months. After several years of service, it is not unusual to find brake fluid contaminated by seven to eight percent water.

Unlike other hydraulic fluids, brake fluid does not flow throughout the system. Brake fluid simply moves slightly back and forth for most of its life, leaving no opportunity to circulate through a heat exchanger of filter. Because it can't be filtered, brake fluid must hold contaminants in suspension to prevent corrosion and clogging of small passages.

It is recommended that you change brake fluid on a regular basis to remove accumulated water and other contaminants, preserving the life of brake system components and increasing the performance and reliability of the brake system.

Applications

Consult the AMSOIL Online Product Application Guide for application information. For power sports applications, consult the owner's manual to determine the correct DOT classification. 

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