Which Brake Fluid is best for My Car?

When was the last time you checked your brake fluid? If you’re struggling to remember, you’re not alone. Many drivers often forget about checking this crucial vehicle fluid.

Brake fluid is often overlooked in vehicle maintenance, which is quite ironic given that it’s crucial for stopping your car and preventing accidents, and comes in handy at corners.

Knowing how brake fluid functions is key to understanding its maintenance requirements. This becomes even more vital if you have a newer car equipped with modern braking systems like ABS/ESP or other brake assist technologies.

In this article, we’ll dive deep into the world of brake fluid. You’ll learn about how it functions, the various kinds available, and other vital details. By the end of our discussion, you’ll be well-informed about everything related to brake fluid.

What is Brake Fluid?

While most people understand that brake fluid is the hydraulic fluid operating a vehicle’s brakes, there’s more to its role. A typical braking system includes a variety of components like hard and soft lines, brake cylinders, calipers, and ABS modules, varying with different vehicles.

Brake fluid does more than just activate the brakes; it also plays a crucial role in preventing these components from corroding. Vehicle manufacturers count on the presence of brake fluid in the system to combat corrosion. However, there’s a catch.

Brake fluid is hygroscopic, meaning it naturally absorbs moisture from its surroundings. This characteristic is the main reason why regular maintenance of brake fluid is essential. Without it, manufacturers could potentially create a closed, maintenance-free braking system.

What’s the best brake fluid for your car?

You should always use the brake fluid as recommended in your vehicle manual or maintenance guide, this will provide a DOT rating for the correct fluid but what does that mean?

Brake Fluid Department of Transport (DoT) ratings

Have you ever questioned the meaning of DOT ratings on brake fluids? These ratings, established by the United States’ Department of Transport (DOT), are key indicators of a brake fluid’s performance, including its boiling points in both wet and dry conditions. These ratings are prominently marked on the fluid’s packaging. Brake fluids fall under specific DOT classifications: glycol-based fluids like DOT3, DOT4, and DOT 5.1, as well as DOT5, which is silicone-based. Generally, a higher DOT rating means a higher boiling point. However, it’s crucial to consult your vehicle’s handbook to determine the appropriate fluid for your car.

DOT 2 is the earliest DOT rating and is now virtually obsolete. Fluids in this category have a dry boiling point of 190°C, which doesn’t suit modern braking systems.

DOT 3 is a glycol-based fluid primarily used in older vehicles. It has a dry boiling point of 205°C or 446°F.

DOT 4 is currently the standard, though it’s gradually being replaced. It’s compatible with DOT 3, contributing to the latter’s obsolescence. DOT 4, also glycol-based, includes Borate esters for enhanced performance.

DOT 4+ is an advanced version of DOT 4, featuring a higher dry boiling point. It’s commonly used in racing vehicles for its ability to withstand the rigors of continuous braking cycles without boiling.

DOT 5, surprisingly, isn’t designed for active braking systems. This silicone-based fluid is more suited for show vehicles as a preservative than as a functional brake fluid. Using DOT 5 in a regular street vehicle could lead to brake failure.

DOT 5.1, despite its name, differs significantly from DOT 5. It’s a glycol-borate based fluid with a high dry boiling point of 270°C/500°F. It’s backward compatible with DOT 4 and DOT 3 and has become the new standard for most vehicles.

Understanding Brake Fluid Wet and Dry Boiling Points

Every type of brake fluid has two boiling point ratings: dry and wet. The dry boiling point indicates the maximum temperature the fluid can reach when it’s new and pure, straight from an unopened container.

The wet boiling point, on the other hand, reflects the fluid’s temperature limit after it has absorbed 3.7% water by volume. When the DOT standards were established, a 3.7% water content was considered the typical level for fluid that had been in use for about 2 years.

This means the wet boiling point essentially measures how the fluid’s performance degrades over a typical maintenance cycle.

If the fluid remains in the system for more than 2 years, the water content can increase, lowering the wet boiling point. While this degradation may not be noticeable during regular city driving, the impact of contaminated fluid becomes evident during intense braking situations.

What happens when moisture gets into brake fluid?

When your brake fluid begins to absorb moisture, it leads to two main issues. Firstly, the effectiveness of the fluid in operating the brakes decreases. If there’s a lot of moisture, the fluid can boil under heavy use. When it reaches its boiling point, its capacity to activate the calipers, the ABS, and other crucial systems is significantly reduced. This makes the fluid both unsafe and inefficient.

Secondly, the presence of moisture in the fluid can lead to corrosion of the braking system’s components. These parts depend on clean fluid to prevent rusting. Introducing water into the system heightens the risk of corrosion.

DOT 5 brake fluid is silicone-based and does not absorb water. This type of fluid is incompatible with other brake fluids and is primarily used in classic cars that are stored for extended periods. Its ability to resist water absorption makes it ideal for such vehicles.

Brake Fluid should be changed every 2 years.

Brake fluid should be changed every two years primarily due to its hygroscopic nature, which means it absorbs moisture from the environment. Over time, this moisture accumulation leads to a significant reduction in the fluid’s effectiveness. The wet boiling point of brake fluid, which indicates its maximum temperature after absorbing 3.7% water by volume, is a key factor to consider. Typically, this level of water contamination is reached within two years under normal driving conditions.

As the water content in the brake fluid increases, its boiling point decreases, which can compromise braking performance, especially under heavy use. This moisture also contributes to internal corrosion within the braking system. Regularly changing the brake fluid every two years helps maintain optimal braking performance and prevent long-term damage to the brake system components.

How to change Brake Fluid yourself

Changing the brake fluid in your car is an important maintenance task. Here’s a simplified guide on how to do it:

1. Gather Your Tools and Supplies: You’ll need new brake fluid (as specified by your car manufacturer), a wrench (usually a lug wrench or socket wrench), a brake bleeder kit or a clear tube and a catch container, and a helper if possible.
2. Safety First: Ensure your car is parked on a level surface, and the engine is cool. Engage the parking brake and open the hood.
3. Locate the Brake Fluid Reservoir: It’s usually on the driver’s side of the vehicle, near the firewall.
4. Check Fluid Level and Quality: Before you start, check the current fluid level and its condition. Dark, dirty fluid needs replacing.
5. Prepare for Bleeding: Start with the wheel furthest from the master cylinder (usually rear passenger side), then work your way to the closest (front driver’s side). Attach the tube from the bleeder kit to the bleed valve and place the other end in a container.
6. Flush the System: Have your helper press down on the brake pedal. Open the bleed valve slightly to let old fluid and air out. Close the valve, then release the brake pedal. Repeat this process until clean fluid comes out. Make sure the reservoir doesn’t run dry. Repeat for each wheel.
7. Refill with New Fluid: Once all lines are flushed, top up the master cylinder with fresh brake fluid to the correct level.
8. Check for Leaks and Test: After you’re done, check for any leaks around the bleed valves. Start your car and press the brake pedal a few times to ensure it feels firm, not spongy.
9. Dispose of Old Fluid: Brake fluid is toxic and must be disposed of properly. Do not pour it down the drain; take it to a recycling center or automotive shop.