Can DOT 3 brake fluid be used on DOT 4 recommended brake fluid systems?
The short answer is no, DOT 3 brake fluid should not be used in a brake system that requires DOT 4 brake fluid. DOT 3 and DOT 4 brake fluids have different specifications and using the wrong type can potentially damage the brake system.
Understanding DOT 3 and DOT 4 Brake Fluids
Brake fluids are classified by the Department of Transportation (DOT) based on their boiling points and other performance characteristics. DOT 3 and DOT 4 are the two most common types of brake fluids used in modern vehicles.
- DOT 3 Brake Fluid: Has a lower boiling point and is generally recommended for lighter-duty brake systems. It has a minimum dry boiling point of 401°F (205°C) and a minimum wet boiling point of 284°F (140°C).
- DOT 4 Brake Fluid: Has a higher boiling point and is recommended for more demanding brake systems, such as those found in high-performance vehicles. It has a minimum dry boiling point of 446°F (230°C) and a minimum wet boiling point of 311°F (155°C).
The higher boiling points of DOT 4 fluid allow it to better withstand the high temperatures generated during heavy or repeated braking, reducing the risk of brake fade.
Why DOT 3 Brake Fluid Should Not Be Used in DOT 4 Systems
Using DOT 3 brake fluid in a DOT 4 brake system can be problematic for a few reasons:
- Boiling Point Mismatch: The lower boiling point of DOT 3 fluid means it is more susceptible to boiling under high-heat conditions, which can lead to a loss of brake fluid and potentially cause brake failure.
- Compatibility Issues: DOT 3 and DOT 4 fluids are not always compatible with each other, and mixing them can cause the brake system components to deteriorate over time.
- Reduced Performance: The lower-quality DOT 3 fluid may not provide the same level of lubrication and corrosion protection as the DOT 4 fluid specified by the vehicle manufacturer, potentially leading to reduced brake performance and lifespan.
To ensure the safety and proper functioning of your vehicle's brakes, it is crucial to use the brake fluid type recommended by the manufacturer, which is typically DOT 4 for many modern cars and trucks.
Why use DOT 3 over DOT 4?
If you wanna get technical, DOT 3 will absorb less water and is cheaper then DOT 4. DOT 4 will have a higher boiling point then 3. The difference is minimal at best & doesn't really matter what one you choose.
What happens if you put DOT 3 brake fluid in a DOT 4 system?
Putting DOT 3 in a DOT 4 system will lower the braking performance and boiling point of the fluid, increasing the risk of brake fade and failure, especially under heavy use or in hot weather. While the fluids are compatible and won't immediately damage the system, it's not recommended because DOT 4 is designed with a higher boiling point for safety, and using a lower-grade fluid negates that advantage.
Effects of using DOT 3 in a DOT 4 system
- Lowered boiling point: DOT 4 fluid has a higher boiling point than DOT 3. Mixing them will lower the overall boiling point of the brake fluid in your system.
- Increased risk of brake fade: If the brake fluid boils, it creates vapor bubbles in the brake lines, which are compressible. This leads to a spongy brake pedal and reduced braking ability, a condition known as brake fade.
- Potential for brake failure: In extreme situations like driving down a long, steep mountain pass or during heavy use in hot weather, the lower boiling point of the mixed fluid can lead to brake failure.
- Performance compromise: While not an immediate danger, using DOT 3 in a system designed for DOT 4 results in a compromise of the braking system's performance and safety margin.
What to do
- Avoid it: Ideally, you should not use DOT 3 in a DOT 4 system. If you have already done so, it's best to have the system completely flushed and refilled with the correct DOT 4 fluid.
- Replace the fluid: To ensure safety, completely flush the old fluid and replace it with the recommended DOT 4 fluid.
- Consider your driving habits: If you perform a lot of heavy braking, live in a hot climate, or frequently tow heavy loads, using a lower-grade fluid like DOT 3 is particularly risky.
What is DOT 4 compatible with?
Brake Fluid DOT 4 is compatible with other brands of DOT 4/DOT 3 brake fluid. Brake Fluid DOT 4 should not to be used in systems designed for mineral oil based fluids (LHM), for example certain Citroën models, or where Silicone DOT 5 fluids are recommended.
Can I mix different colors of brake fluid?
Brands do not matter. Brake fluid is rather simple in design. Dot 3,4, and 5.1 can all be mixed. The difference is, as the number increases, so does the boiling point of the fluid. So if you mix Dot 3and Dot 5.1, it will work, but you wasted money on the 5.1 because now it has a lowere...
