Can You Mix Dot 3 And Dot 4 Brake Fluid

can you mix dot 3 and dot 4 brake fluid

Brake fluids are key in transmitting the pressure applied on the brake lever to the brake pads and other braking system components. These brake fluids are made to be non-compressible. This means they can transmit the pressure effectively.

The most common options would be DOT 3 and DOT 4. There is also DOT 5, which is seen as the newer version, but the others still have plenty of applications.

On whether you can mix DOT3 and DOT4, YES, it is possible to do that, but just know you have altered the boiling point of the resultant fluid. It is why you should always use one type of brake fluid to ensure the braking system continues to work correctly.

What is a DOT Brake Fluid?

The DOT in the names of these brake fluids means Department of Transport. This means that the brake fluid has met the stringent specifications of the Society of Automotive Engineers and the Department of Transport. So, it should be safe for you to use in the braking system.

The brake fluids DOT 3 and DOT 4 would be made of the poly-glycol base. Such a base is a mixture of many ingredients that make the final product.

These ingredients are grouped as follows;

  • Inhibitors are key to preventing corrosion and oxidation
  • Modifier couplers are essential for changing the intensity of swelling for the exposed rubber parts
  • A solvent diluent is essential to determine the viscosity and the brake fluid’s boiling point. This accounts for 40 to 80% of the brake fluid.
  • Lubricants such as polyethylene and polypropylenewill keep the parts moving with ease. It can account for 20 to 40% of the fluid.

Here is a video explaining the brake fluid basics you should know

What is DOT3 Brake Fluid

The DOT3 brake fluid is designed for many applications, including brake and clutch applications. The product is made by mixing glycerin and alcohol to end up with a brake fluid that is non-silicone, fully synthetic, and non-mineral based.

The biggest advantage of DOT 3 brake fluid is that it comes with a high boiling point. This makes it safe and helps it deliver consistent performance even when the braking pressure is increased. Also, the high boiling point means it can withstand high and cold temperatures without necessarily thickening.

Another important thing to note is that the rubber component swell in this fluid is kept to a minimum. This helps reduce fluid loss and leakages too. The result is that you should end up with excellent corrosion protection generally.

The DOT 3 brake fluid can be found in most auto-part stores and would be good for refills or top-ups for clutch and brake systems in passenger cars, motorcycles, and heavy commercial vehicles. You could still use them in construction, mining, and agricultural equipment.

We recommend you use it only if that is what the vehicle manufacturer specifies. Take note that the fluid is also hygroscopic. This means it can absorb water from the air, thus lowering its effectiveness. So, ensure you reseal the cap tightly after using it to keep the water out.

What is DOT 4 Brake Fluid

DOT 4 brake fluids are based on glycol-ether as the main ingredient and have borate esters too. This improves their performance quite a lot. That is why you will find the DOT 4 brake fluid has a higher and more stable boiling point than DOT 3 brake fluids.

It has a dry boiling point of 230 degrees Celsius and 155 degrees Celsius for the wet boiling point.

It is advisable to change the DOT4 brake system after two years. This is to help maintain the safety and performance of such a brake system. Note that the lifetime of the brake system is affected when the fluid absorbs water. So, make sure any leaks are contained to avoid such scenarios.

When you fail to change the fluid within the recommended timeframe, you might end up with corroded master cylinder parts and wheel cylinders.

DOT3 vs. DOT4 Brake Fluid

DOT3 vs. DOT4 Brake Fluid

For a while now, DOT 3 has been the most popular because of its availability and affordability. It is also good in terms of performance, and you do not need to change it more often. Of course, the rise of DOT 4 has also made it quite interesting to see the two competing against each other. That is why we want to see what makes them similar and different below.

  • Chemical structure

These two are different in terms of their chemical structures. DOT3 is achieved by blending ether and polyethylene while DOT4 is through mixing glycol and borate.

Using ether combined with glycol makes DOT3 quite good for hot and wet conditions. That is why it is popular in regular vehicles.

DOT 4 still has several benefits, thanks to its formula. We find that it offers a higher tolerance to water and can remain stable under very high temperatures.

  • Boiling points

Another big difference between these two would be the boiling point. We find that DOT 3 features a lower boiling point. This makes it assimilate to water easily. So, expect it to boil faster when put through hard and rough braking conditions.

DOT 4 has a higher boiling point. This makes it a good alternative for the DOT 3 brake fluid systems. However, you cannot use DOT 3 as an alternative to DOT 4 because of reduced performance.

  • Boiling capacity

We find that DOT 3 brake fluid features a great wet and dry boiling point. This means it would still work more amazingly when exposed to water and air than DOT 4. However, DOT 4 still has a better dry boiling capacity with its own applications.

Here is a video with several differences between DOT 3 and DOT 4 you should know


What is the price of DOT 3 and DOT 4 brake fluids?

Expect DOT 3 to cost $13 to $16 while DOT 4 would cost $15 to $19. They are relatively affordable than DOT 5, which can cost up to $45.

What happens when you mix DOT 4 and DOT 3 brake fluids?

These brake fluids are generally compatible with each other; thus, you will not have a problem when you mix them. However, it would mean that the resultant mixture of the two will now have an unpredictable boiling point performance.

When should you use DOT 4 brake fluid?

This type of brake fluid is recommended for applications that need vigorous braking actions, such as racing cars and police vehicles. This is because the fluid has a higher boiling point.

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