Why and How Often Does Brake Fluid Need to Be Changed?
Brake fluid is a commonly overlooked but extremely important part of vehicle performance. Brake fluid has only one job- to stop your vehicle. The hydraulic fluid transfers the pressure applied to the brake pedal to the brake calipers or drums by way of brake lines. Since brake fluid must function without failure, the Department of Transportation regulates the performance qualities of brake fluid. A few of the standards for brake fluid are:
- Remain fluid at low temperatures
- Resist boiling at high temperatures
- Compatible with other parts of the braking system
- Must not contribute to brake system corrosion
How is Brake Fluid Rated?
The Department of Transportation has been tasked with rating brake fluid and providing a classification system for different types.
Most vehicles in the USA are designed to run with DOT3 or DOT4. These brake fluids are amber-colored and glycol-based. They absorb moisture and should not be unnecessarily exposed to air. As the brake fluid is used, it will eventually degrade and become acidic because of moisture and high temperatures. It must be changed periodically to avoid corrosion within the braking system.
Many European car manufacturers call for DOT4 brake fluid to be used in their vehicles. DOT4 has a higher boiling point than DOT3, which helps to reduce the degradation of the fluid. There are different types of DOT4 brake fluid depending on your vehicle:
- Standard DOT4
- DOT4 Plus
- DOT 4 Low Viscosity
A silicone-based brake fluid with a very high boiling point, DOT5 is typically purple. It doesn’t absorb water, reducing corrosion, but can become foamy with lots of air bubbles. DOT5 is never used with ABS systems.
Priced at about 14x more than DOT3, DOT5.1 is a premium brake fluid that has been historically used by the racing industry. It is glycol-based but is very light, meaning that the moisture pools at the lowest point. DOT5.1’s properties make it a good choice for vehicles used for driving in severe conditions.
When Should Brake Fluid Be Changed?
When vehicle owners experience brake failure, it is typically related to one or more of these issues:
- The brake fluid has degraded and no longer allows the transfer of pressure to activate braking.
- Moisture is in the brake fluid and has caused brake components to corrode.
- Brake fluid has become contaminated with debris that leads to brake failure.
All of these issues can be prevented with a routine brake fluid exchange. During a brake fluid exchange, the old brake fluid is drained, debris is removed, the braking components are checked for rust and other damage, and then new brake fluid is added.
Although different vehicle manufacturers specify different time frames for brake fluid replacement, they are typically recommended every two years or 30,000 miles. If most of a vehicle’s driving is on long stretches of highway, the brakes may not be used as much and the fluid may not require replacement as often. A vehicle that drives mostly in a city environment may need more frequent brake fluid flushes.