Apart from the engine, the brakes are one of the most crucial systems in any vehicle. There is no point in going fast if you can’t stop just as quickly. The brake system is composed of several elements like brake pads, calipers, and rotors. However, none of these systems can function without brake fluid. Speaking of brake fluid, there is a large selection of products to choose from. DOT 3 and DOT 4 are two of the most popular brake fluid types out there. But, can you mix DOT 3 and DOT 4? If you don’t know the answer, you have come to the right place.
As time goes on, ultimately there will come a point where you’ll have to change the brake fluid of your vehicle. When that time comes, knowing the differences between the different types of brake fluid as well as whether they can be mixed will surely come in handy. After going through this article, you’ll have answers to all these burning questions.
Before looking at the mixing properties of different brake fluids, we thought of taking a look at what brake fluid is as well as its properties. So, let’s get started, shall we?
What Is Brake Fluid
Brake fluid is made up of a liquid chemical solution. It is an important part of the hydraulic braking systems that come equipped in almost all modern vehicles. The brake fluid amplifies the force exerted by your foot on the brake pedal and turns it into brake pressure.
There are a few components that work together in this process. First, the vacuum booster behind the brake pedal enhances the force exerted by your foot. Then, this pressure activates the master brake cylinder. It releases the pressurized brake fluid into the brake lines, activating the brakes in the process.
When the brake fluid reaches the calipers, it pushes the pistons with great force. The pistons push against the brake pads, which in return rub against the rotors. This results in friction, which ultimately slows the vehicle down and brings it to a stop.
However, you can find a variety of brake fluid types out on the market. One thing that is common among all these varieties is the DOT classification system. Are you curious about the DOT naming system? Well, you’re in luck! We will tell you all about it in the next section of this article.
DOT is an acronym for the U.S. Department of Transportation. This organization has classified brake fluid into different types, which makes it easier for the customers to distinguish them from each other. Throughout the years, there have been multiple DOT classifications including DOT 1, DOT 2, DOT 3, DOT 4, and DOT 5.1. However, DOT 1 and DOT 2 brake fluids are no longer used in modern vehicles.
Although DOT is the most popular brake fluid classification, it is not the only one out there. The International Standards Organization (ISO) and the Society of Automotive Engineers (SAE) also have their own classifications for automotive brake fluid.
At present, DOT fluid is the most commonly used brake fluid around the globe. With the exception of DOT 5, all other brake fluids are composed of a poly-glycol base.
In other words, DOT brake fluids are made up of a mixture of around ten ingredients. However, this larger variety of materials can be broken down into four main components. They are,
- Inhibitors – The purpose of inhibitors is the prevention of corrosion and oxidation.
- Modified Coupler – The intensity of swelling on the rubber components exposed to the outside is done by the modified coupler.
- Lubricant – Ensures that all parts are moving freely from 20% to 40%. Common lubricants in DOT fluid include polyethylene and polypropylene.
- Solvent Dilutent – 50 to 80 percent of the brake fluid is accounted for by the solvent diluent. Glycol ether is the most widely used material for this purpose, and it is what determines the brake fluids’ viscosity and boiling point.
The Department of Transportation pays close attention to maintaining the performance of the brake fluid at different temperatures. To achieve this purpose, it has set strict standards and specifications.
DOT 3 Brake Fluid
Now you have a clear understanding of the meaning of DOT brake fluid. However, before discussing whether you can mix DOT 3 and DOT 4 brake fluid, it is important that you get to know about these two varieties individually.
DOT 3 brake fluid is made up entirely using fully synthetic materials. As a result, it does not contain any mineral oils or silicone products. Instead, a mixture of glycerin and alcohol is used to make DOT 3 brake fluid. Additionally, the high performance of the fluid is ensured with the use of polyethylene glycol ether technology.
There are several advantages of DOT 3 brake fluid. But, by far the most impressive one is its high boiling point. This ensures consistent performance and safety when high brake pressure is applied.
Not only that, DOT 3 brake fluid has the ability to withstand extreme temperatures as well. In fact, it can endure temperatures as high as 250° C.
On the other hand, DOT 3 brake fluid does not thicken in extremely cold temperatures as well.
Another advantage of DOT 3 brake fluid is its resistance to corrosion. This ensures the longevity of the brake system components and improves reliability as well. Furthermore, the minimal rubber component swell in DOT 3 brake fluid prevents leakages and the loss of fluid over time.
3. Where To Use DOT 3 Fluid
DOT 3 brake fluid offers a number of use cases. Owners of heavy-duty vehicles, passenger cars, 4WD vehicles, and motorcycles can use DOT 3 fluid to top up the clutch and brake systems. Additionally, DOT 3 fluid can also be used in machinery used for agriculture, mining, and construction work.
Although DOT 3 brake fluid is versatile and offers many advantages, you should only use it when the vehicle manufacturer has specified to do so. It is also advised to use protective gear while using brake fluids it can cause skin irritations.
Moreover, paint and varnish surfaces can also be damaged by brake fluid too, so be careful when you are handling it.
Not only that, but when you use DOT 3 fluid, you should pay close attention to its hygroscopic nature. You see, DOT 3 fluid naturally absorbs water particles from the atmosphere. This results in lowered performance. So, make sure to reseal the cap of the DOT 3 fluid container after use to ensure maximum performance in the future.
Similarly, it is important that you get to know the properties of DOT 4 brake fluid as well.
DOT 4 Brake Fluid
DOT 4 brake fluid shares a common trait with DOT 3, which is the use of a glycol ether base in its composition. However, the thing that differentiates this brake fluid from DOT 3 is its use of borate esters. The use of borate esters enhances several aspects of the brake fluid, including performance and the wet and dry boiling points.
When compared to DOT 3, DOT 4 brake fluid has a higher and more stable boiling point. The minimum wet boiling point is 155°C, while the minimum dry boiling point is set at 230°C.
However, DOT 4 brake fluid is known to absorb more moisture through the air and hoses. When this happens, the boiling point falls rapidly when compared to DOT 3 fluid.
Changing the DOT 4 fluid every two years is recommended in order to avoid contamination and maintain maximum performance.
If the DOT 4 fluid has taken on water and not changed for a long time, it can have an adverse effect on the braking system of your vehicle. Components like the master cylinder and wheel cylinders will corrode, and the overall lifespan of the braking system will reduce as well.
DOT 4 brake fluid should only be used if the vehicle manufacturer has specified it. Generally, using this fluid in lower or upper-grade vehicles is not recommended. Racing vehicles and police cars can be listed as some vehicles that use DOT 4 fluids.
DOT 3 VS DOT 4
A number of factors differentiate DOT 3 from DOT 4 brake fluid. Out of them, the boiling points are one of the more significant ones. Not only that, but the hygroscopic nature of the two oils is also different. Generally, DOT 3 brake fluid absorbs more water than DOT 4 fluid, which has an effect on the longevity of the fluid.
Other than these, there are some more differences between DOT 3 and DOT 4 brake fluids. Let us take a closer look at them in the next section.
Difference Between DOT 3 And DOT 4
The differences between DOT 3 and DOT 4 brake fluid go beyond simply the numbers on the labels. Some of the areas where major differences between the two oils are found include,
- Chemical Composition
- Boiling Point
- Boiling Capacity
Can You Mix DOT 3 And DOT 4, Differences #1 – Chemical Composition
It is not required for all brake fluids to be made out of the same materials. So, the composition and structure of DOT 3 and DOT 4 fluids are slightly different from each other. DOT 3 is composed of a mixture of ether and polyalkylene, whereas DOT 4 is made from borate and glycol.
The glycol and ether mixture in DOT 3 oil makes it a great choice for normal vehicles, as it performs well in both cold and hot climates. On the other hand, DOT 4 performs stably under higher temperatures and also tolerates water better than DOT 3.
Can You Mix DOT 3 And DOT 4, Differences #2 – Boiling Point
As we mentioned earlier, the boiling point is another factor where DOT 3 and DOT 4 differ from each other. Out of the two brake fluid types, DOT 3 has a lower boiling point. As a result, DOT 3 oil boils faster under high-stress situations like hard braking. The result can cause damage to the components of the braking system.
On the other hand, DOT 4 brake fluid has a much higher boiling point at 230°C. No matter which brake fluid you choose, water can still contaminate them and degrade the quality. So, it is important to flush the brakes from time to time in order to get rid of the moisture in the system.
Can You Mix DOT 3 And DOT 4, Differences #3 – Boiling Capacity
The boiling capacity determines how well the brake fluid performs when exposed to open air and water. When it comes to this aspect, DOT 3 brake fluid outperforms DOT 4 in both dry and wet conditions. Although DOT 4 fluid has a better dry boiling capacity, its wet boiling capacity leaves much to be desired.
Other than these aspects, the prices of these two brake fluids are also different. DOT 3 fluid is the cheaper of the two, and it can be had for around $13 – $16. In contrast, DOT 4 brake fluid costs between $15 and $19.
Mixing DOT 3 And DOT 4
DOT 3 and DOT 4 brake fluids can in fact be mixed together without worry. That is because both fluids are glycol-based. However, keep in mind that this will have an effect on the overall boiling point.
The two brake fluids can be used in place of each other as well. However, if you own a vehicle that comes from the factory with DOT 4 brake fluid, we don’t recommend filling it with DOT 3. However, vehicles that are recommended to come with DOT 3 fluid can use DOT 4 fluid without any issue.
Additionally, if you own a car that uses DOT 3 brake fluid but your daily commute includes driving on steep hills or towing a trailer, you can instead use DOT 4 fluid for extra peace of mind.
Brake Fluid Color Chart
No matter if you purchase DOT 3, DOT 4, or DOT 5 brake fluid, all of them look the same when they are brand new. All of them should look clear with a slight yellow tint. However, as time goes on, the color gradually turns darker.
If you spot dark brown or black brake fluid in the reservoir, it is time to flush the brakes and replace the brake fluid.
The absorption of grime and water is what turns the brake fluid into a darker shade.
Darkened brake fluid has lower performance, and can cause brake fade as well. We recommend checking the color of the brake fluid as you go through the regular maintenance of your vehicle.
Adding Brake Fluid
Generally, drivers are recommended to change the brake fluid of their vehicles every 2 years or 30,000 miles. But, this time period varies between vehicle manufacturers as well as the type of brake fluid being used.
It is important to change the brake fluid at regular intervals due to several reasons. As we discussed earlier, brake fluid is notorious for absorbing water molecules. Over time, this can corrode parts of the braking system, resulting in hefty repair bills.
The natural breakdown of the brake fluid is another thing that should be considered. As time passes, the chemical properties of the brake fluid also change. This lowers the fluids’ boiling point, which causes the brakes to get hot when they are applied.
If the brake fluid replacement of your vehicle is due, it is not a must to take your vehicle to a mechanic. In fact, the brake fluid can easily be replaced in your home garage. There are several steps that should be followed when replacing the brake fluid.
1. Parking The Vehicle On A Level Surface
The first step in replacing the brake fluid is parking the vehicle on a level surface. This helps in determining the current brake fluid level.
2. Examining The Current Fluid
Next, you should locate the brake fluid reservoir to examine the current fluid level. However, if you own a vehicle with anti-lock brakes, you should depress the brake pedal around 30 times before attempting to replace the fluid.
In most vehicles, the brake fluid reservoir is housed at the back of the engine compartment on the driver’s side. If you have difficulty locating it, all you have to do is to refer to the owner’s manual.
Once you locate it, examine the reservoir to determine whether the fluid needs to be refilled. The minimum and maximum markings on the reservoir should help you in this process.
Another thing you should pay attention to is the color of the brake fluid. Ideally, the fluid should have a light or golden yellow hue. If it is too dark in color, then it might be high time for a replacement.
3. Clean The Reservoir
Your next course of action should be to open and clean the brake fluid compartment. Depending on the car, either unscrew or pull up on the reservoir cap to remove it. Then, clean it using either a paper towel or a worn rag.
If your vehicle comes with any electrical components that measure brake fluid integrity, disassemble and clean them as well. But, keep in mind to disconnect the battery before you get started.
4. Add New Brake Fluid
When you are done with the cleaning, the next step should be to add new brake fluid to the vehicle. Using a funnel will make this process much easier. Simply fill the vehicle with recommended brake fluid until the volume reaches just below the maximum marker. After that, reinstall the electrical components (if there were any) and close the cap tightly to prevent any air from getting in.
You can learn more in our guide on how long do brakes last on a car.
5. Pump The Brakes
The final thing to do after replacing the brake fluid is to pump the brakes. This pushes the brake fluid through the lines and gets rid of any air trapped inside. Not only that but pumping the brakes also pressurizes the brakes system as well. After pumping around 30 times, you will feel the brake pedal engage, which signals that the process has been successfully completed.
Brake Fluid Boiling Point
The boiling point of brake fluid is something that we came across throughout this discussion. Well, this stat is important because brake fluid has to endure a significant amount of heat during its lifetime. When you press the brake pedal, it creates friction, resulting in a lot of heat. Intense heat will cause the brake fluid to boil, hampering its function.
The boiling point is further divided into two parameters, named the dry boiling point and the wet boiling point. The dry boiling point is measured by using brake fluid from a brand-new container. On the other hand, brake fluid that is contaminated by about 3.7% of water is used to measure the wet boiling point.
Can You Mix DOT 3 And DOT 4: In Conclusion…
Brake fluid is essential for the safety and performance of any vehicle. When it comes to passenger vehicles, DOT 3 brake fluid is the type most widely used around the globe.
However, DOT 4 fluid is also used by some modern vehicles and other machinery. Although these two types can be mixed without any major issues, it is important to remember that mixing brake fluids have an effect on their boiling points.
FAQs On Can You Mix DOT 3 And DOT 4
What Is Brake Fluid
Brake fluid is one of the most important liquids in any vehicle. It is a type of hydraulic fluid and it is responsible for transferring force on the brake pedal into pressure. This pressure activates the brakes and slows down the vehicle.
What Is DOT 3 Fluid
DOT 3 is a type of brake fluid used in modern vehicles. It is made using a polyethylene glycol-based solution. DOT 3 brake fluid has a boiling point of around 250° C, and it performs well in both hot and cold temperatures.
How To Put Brake Fluid In Car
Putting brake fluid into a car is something any vehicle owner can do. All you have to do is to locate the brake oil reservoir and fill it up to the maximum level mark. But, remember to pump the brakes once you finish filling it up.
Where To Put In Brake Fluid
Brake fluid should be put into the brake reservoir. It is located under the hood on the driver’s side. Referring to the owner’s manual will point you toward this component.
What’s The Difference Between Dot3 And Dot4 Brake Fluid
There are several differences between DOT 3 and DOT 4 brake fluids. The main ones include their boiling point, chemical composition, boiling capacity, and the amount of water they absorb. DOT 3 and DOT 4 fluids differ in price as well. Generally, DOT 4 fluid is more expensive when compared to DOT 3.