Can You Mix DOT 3 and DOT 4? (Read First)

Can you mix DOT 3 and DOT 4 Brake Fluid? This is a common question asked by vehicle owners who want to replace or top up their brake fluid.

If you are looking for the answer to this question, you are on the right page because this article contains the answer you need and more.

Read on to find out if you can mix DOT 3 and DOT 4 brake fluid, the difference between both brake fluids, how compatible they are, and lots more.

If you use a factory-filled DOT 3 brake fluid on your vehicle and frequently drive on a steep hill or with a trailer, refilling a DOT 4 brake fluid is highly recommended.

Also Read: How Much Brake Fluid Do I Need?

DOT 3 vs DOT 4: Brake Fluid Differences

Can You Mix DOT 3 and DOT 4

The boiling point is the significant difference between the DOT 4 and DOT 3 brake fluids. The DOT 4 fluid is best for higher performance because of its higher dry and wet boiling point.

Glycol-based brake fluids have different numerical categories, such as 5.1, 5,4,3, etc. Although the brake fluid has no standard formula, the government has set specific standards, and the brake fluid has to meet these standards.

The standards cut across various categories such as oxidation resistance, water tolerance, chemical stability, and pH values.

DOT 3 is the most preferred brake fluid for regular drivers. It is most suitable for cars that don’t use their brake system aggressively.

DOT 4 is commonly used in racing and police cars because its boiling point is higher. DOT 3 is not compatible with DOT 4, whereas DOT 4 has high compatibility with DOT 3.

1. Varying Boiling Points (BP)

The significant difference between DOT 4 and DOT 3 fluid is their Boiling Point. The boiling point refers to the temperature that results in the fluid evaporation. This factor also affects their water absorption level, but they are both hygroscopic.

DOT 3 has tendencies of water absorption since its boiling point is lower. Therefore, hard braking tends to cause boiling.

Boiling points are of two types:- wet and dry. The dry can be referred to as the boiling point of brake fluid from a new bottle that any water molecule has not contaminated, and the wet can be referred to as the boiling point of brake fluid with at least a 3.7% water contamination.

The wet boiling point takes place during everyday driving. The quality gets degraded each time you put brake fluid in the reservoir. Hence, the brake system must be flushed regularly to ensure it remains in good condition.

2. Boiling Capacity

There is also a need to discuss the boiling capacity difference. DOT 3 has both dry and wet boiling capacities to function appropriately in both open-air and water. DOT 4 can not function properly in water but has an excellent dry boiling capacity.

Standard vehicles use more DOT 3, but DOT 4 is preferable in racing cars or vehicles used for rough driving adventures because it safeguards your brake system.

3. Chemical Structures

The DOT 4 and DOT 3 equally vary in chemical structures. The DOT 3 is mainly centered on diethylene glycol (DEG). Although this isn’t a requirement, most brake fluid producers have adopted it.

DOT 4 consists of borate ester and glycol, which helps the liquid withstand higher temperatures. There is a tendency for higher wet and dry boiling points, and the chemical components help in facilitating a high water tolerance level and high-temperature stability.

Also Read: Low Brake Fluid Symptoms (+ How to Fix)

Are DOT 3 and DOT 4 Brake Fluid Compatible?

DOT 3 and DOT 4 brake fluids are compatible. However, the boiling point of DOT 4 is higher.

Due to the high BP of DOT 5.1, it is used in heavy-duty and high-performance applications. In addition, it is compatible with DOT 4 and DOT 3 fluid.

The brake fluid of DOT 5 is silicone, which means it does not absorb water. Therefore, it has zero compatibility with other brake liquids, and it is used mainly in classic vehicles that are kept in storage or have not been used for a long time and require brake fluids with zero water absorption.

Can You Mix DOT 3 and DOT 4

Can You Mix DOT 5 With DOT 3 and DOT 4?

The ‘DOT5’ brake fluid is silicone-based. It has no compatibility with the ABS systems and doesn’t absorb air moisture. However, it works well and maintains its standards. Its boiling point is higher than that of DOT 4 and DOT 3, making it suitable for excessive rough driving.

Meanwhile, it would be best to never mix DOT 5 brake fluid with DOT 4 or DOT 3 fluids because they are incompatible. Instead, follow instructions from your vehicle manufacturers to know if DOT 5 is suitable for your brake components.

Cautions to Take When Mixing Brake Fluids

When dealing with brake fluid, you have to be cautious. Be watchful so that you won’t spill the two varieties on your vehicle’s body because it can damage your paint.

Break fluids can be dangerous when mixed with different or other liquids. Brake fluids should be stored in a container that is sealed tightly. Also, note that air moisture can cause degradation to the fluid’s chemical components, so do not use brake fluid taken from an uncovered container.

Also Read: Is Brake Fluid Flammable? (Why You Should Be Careful With Them)

Frequently Asked Questions – Can You Mix DOT 3 and DOT 4

What happens if I mix DOT 3 and DOT 4 brake fluid?

DOT 4 and DOT 3 brake fluids are both glycol-based; they are well-matched so that you can mix them.

Are DOT 3 and DOT 4 Brake Fluid Compatible?

DOT 4 and DOT 3 brake fluids are very compatible. However, the boiling point of DOT 4 is higher.

Can you mix brake fluid types?

You can easily mix DOT 5.1 and DOT 4 brake fluids without causing harm to your braking system because they are glycol-based, making them compatible. Also, remember that DOT5.1 differs from DOT 5. While DOT 5.1 is glycol-based, DOT 5 is silicone-based and is incompatible with any brake fluid.

Which brake fluid is better, DOT 3 or DOT 4?

The DOT 4 is a better brake fluid. Various factors differentiate the two, including DOT 3 fluid absorbs less water from the atmosphere than DOT 4 over time; this means you will need a less frequent fluid change. In addition, the wet and dry boiling points of the DOT 4 fluid is higher, making it suitable for high temperatures.

Should I use DOT 3 or DOT 4 brake fluid?

The significant difference between the DOT 3 and DOT 4 brake fluids, as discussed earlier, is that the minimum wet and dry boiling points of a DOT 4 fluid are higher, making most vehicle manufacturers endorse DOT 4 over DOT 3 because it offers an added safety margin.

What happens if you use the wrong brake fluid?

Using the wrong brake fluid could lead to overheating, transmission failure, and poor lubrication. The damage caused may not get reversed, even by flushing the transmission system. Adding brake fluid or motor oil mistakenly can equally destroy the transmission system.

Can DOT 3 be used for power steering?

The DOT 3 fluid is glycol-based, so you can not use it. It will destroy the rubber seals and cause the power steering pump to get damaged due to low lubrication.

Conclusion – Can You Mix DOT 3 and DOT 4

If your car requires DOT 4 or DOT 3 and you are wondering if you can mix the two, the answer is Yes, you can mix the two.

Although you can mix the two without causing harm, it is advisable to follow the manufacturer’s recommendations.

Most drivers prefer using a DOT 4 fluid to DOT 3 because its performance is better. However, under normal driving conditions, DOT 4 is not needed.

The DOT 5.1 brake fluid performs well but cannot be mixed with other brake fluids.

Share your thoughts with us below; which DOT fluid do you think is the most preferable for you?

Scott Greene is a seasoned automotive technician for over 5 years and has been deep into advanced automotive diagnostics for a couple of years. He Loves writing about Automotive Diagnostics and Repair, Trouble codes, Buyer guides for various car parts and accessories, and lots more. 

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