DOT 3 Brake Fluid: Information, Composition and Usage (2023)

DOT 3 Brake Fluid

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Well, DOT 3 brake fluid is a glycol-based brake fluid, and the go-to brake fluid for most vehicles on the roads today.Keep reading for more about this brake fluid, its uses and non-uses. Whether you have the drum brakes or the disk brakes, the force needed to stop the vehicle comes from the brake fluid. And thanks to the technological advancements and changes made of the years, the modern vehicle uses a hydraulic brake fluid derived from alcohol.

Why alcohol?

DOT 3 Brake Fluid: Information, Composition and Usage (1)

Well, the use of alcohol comes from its ability to work even in extreme temperature conditions. Thanks to the use of alcohol-based brake fluids, you don’t have to worry about the brake fluid freezing.Freezing of the brake fluid only happens in conditions under -40 degrees Fahrenheit.And in the dry conditions, the brake fluid could withstand temperatures as high as 400 degrees Fahrenheit, or even higher. Information about how much heat the brake fluid can withstand is important because the brakes operate under high temperatures.

What does the DOT rating on brake fluid mean?

The temperature resistance of brake fluids is the factor that gives rise to different classes of brake fluids. To ensure that the brake fluid you use is ideal for the prevailing conditions around the use of the vehicle, the Department of Transportation (DOT) rates the brake fluids depending on the fluid’s temperature resistance.

So, if you’ve been wondering about where the DOT resistance on the brake fluid comes from, know that it comes from the US Department of Transportation’s that issues all the details on the standards of the different motor vehicle fluids in the company.

DOT 3-brake fluid is a glycol-based brake fluid.Thanks to the glycol (alcohol) component, this fluid is hygroscopic, and it absorbs all moisture from the brake fluid. DOT 3 is also the most common brake fluid used in domestic, as well as the Asian vehicles. But, not all Asian or European cars use DOT 3 brake fluid, and a good number actually use DOT 4 brake fluid.

The popularity of the DOT 3 brake fluid also comes from this brake fluid having the standard measurements necessary for your vehicle’s normal braking system. This brake fluid has the capacity to handle the heat. It also functions in wet and dry conditions, also allowing the fluid the capacity to handle the high heat conditions in the brake system. Note that DOT 3’s brake fluid ability to handle the high heat in wet or dry conditions comes from its structure – DOT 3 brake fluid is made of ether and glycol. Glycol gives the brake fluid its affinity for water.

Boiling points

In dry conditions,DOT 3has a minimum boiling point of 401F and 284F in wet conditions, against DOT 4’s boiling point of 446F and 311F in dry and wet conditions respectively.Although this boiling point is lower than that of DOT 4 brake fluid, it’s enough to enhance the function of the brake fluid in vehicles that do not require aggressive braking.

Remember that the brake fluids are largely differentiated by their boiling points, and the brake fluids with the higher DOT number has a higher the boiling point.

Besides the boiling points, the brake fluids are also differentiated by hygroscopy or the affinity of the brake fluid to hold water. DOT 3 brake fluid has a high hygroscopic level compared to DOT 4 and DOT 5 brake fluids.

Regarding viscosity, DOT 3 brake fluid has a relatively low viscosity of 1500 at -40F while DOT 4 has a viscosity of 1800 at the same temperature.

Are all DOT 3 brake fluids compatible?

No, not all DOT 3 brake fluids are compatible.Although you’d expect all brands of DOT 3 brake fluid to be compatible with each other, this is hardly the case. The fluids often have subtle differences that affect the function of your vehicle’s performance.

(Video) Brake Fluids Explained: Types, Compatibility, & Lifespan!

Note that besides the glycol-based brake fluids, there are mineral-based brake fluids, which means that you should only mix two DOT 3 brake fluids if you’re certain that their chemical components are exactly similar.

Most of the DOT 3 brake fluids on the market today are synthetic.

The applications of DOT 3 Brake Fluid

The DOT 3 brake fluid is an essential part of the automotive disc, the clutch system, and the anti-skid brake systems. It’s also an important part of your vehicle’s drum.

For the best effects, you need to consider these recommendations:

  • Only use the brake fluid in its concentrated form, from a concentrated and a previously unopened container.
  • After use, always seal off the brake fluid container. This is an important thing because your DOT 3 brake fluid is hygroscopic and it absorbs moisture from the atmosphere rapidly, resulting in a significant reduction in the service life of the brake fluid.
  • Also, you should never reuse brake fluid in the event of a spillage, you should remove/ wipe off spillages immediately and without rubbing on it because the brake fluid will cause permanent damage on your vehicle’s paintwork.

What Is DOT 3 Brake Fluid Made Of?

DOT 3 is an alcohol and glycerin mixture, also called glycol mixture.It’s also made of extra additives that give the brake fluid the extra kick/ robustness needed to give the brake fluid its power and effectiveness.

DOT 3, like all the other brake fluids, are made of three maincomponents, the solvent, the lubricant, and the additives. The solvent makes up 60-90% of the brake fluid, the lubricant constitutes 5-30%, and the additives make up between 2 and 5% of the brake fluid.

Keep in mind that the glycols that make up the DOT 3 brake fluid represent a mixture of alcohol-based and non-petroleum fluids. The mixing of these fluids forms the polyglycol that DOT 3 brake fluid is known for.

Despite DOT 3’s recommendation as the best brake fluid for passenger vehicles and small vehicles, note that the fluid will not last forever and you need to replace the fluid as recommended. Being hygroscopic, excess moisture accumulation results in the corrosion of the brake system, which could leave you with a spongy pedal or worse issues like vapor lock.

Can I Top Up DOT 3 Brake Fluid with DOT 4?

Brake fluid is the hydraulic fluid necessary for the activation of a vehicle’s braking system. The braking fluid lubricates the components of the braking system, ensuring that the entire system responds promptly when pressing the brake pedal.

With the right braking fluid, the piston compresses the rotors to slow down your car comfortably.

Out of the four categories of brake fluids approved by the US Department of Transportation, DOT 3 and DOT 4 are the main categories of brake fluids. The others are DOT 5 and DOT 5.1.

DOT 3 and DOT 4 are glycol-based fluids, but choosing the right braking fluid means looking at the characteristics of each braking fluid to ensure that you have the right fluid in your vehicle.

But, what happens when you have DOT3 brake fluid vehicle and DOT4 braking fluid.

Can you top up DOT 4 braking fluid to DOT 3 braking fluid vehicle?

Yes. The two braking fluids are compatible with each other. But before you get too excited, DOT 4 is only compatible with DOT 3, not the other way around.

The reason for this difference in compatibility is that DOT 4 has a higher boiling point than DOT 3.

What is the difference between DOT3 and DOT4 brake fluids?

Between DOT 3 and DOT 4, DOT 3 is more common among daily drivers of cars and trucks since these vehicles don’t make use of the braking system aggressively. DOT 3 braking fluid cannot handle too much heat, hence its use in daily and non-aggressive braking systems that don’t convert kinetic energy into thermal/ heat energy.

DOT4 braking fluid, on the other hand, is ideal for use in racing cars and police vehicles requiring aggressive braking, and it’s gained popularity over the past few years thanks to its traction control and the anti-lock braking system. DOT4 braking fluid also has a lower viscosity than DOT3 braking fluid.

But these are not the only differences between the two brake fluids. The brake fluids also differ in their boiling capacity, boiling point, and chemical structure.

Boiling Point

The main difference between DOT 3 and DOT 4 is their boiling points, or rather the fluid’s tenacity in absorbing water. DOT 3 has a lower boiling point, and it takes up more water than DOT 4. Therefore, this braking fluid will boil easily in the rough and hard braking conditions, resulting in irreparable damage to the braking components. Aggressive braking could also result in the sub-par performance of the braking system.

Therefore, you could use DOT 4 braking fluid in place of DOT 3, but you cannot use DOT 3 in place of DOT 4. A vehicle using DOT 3 brake fluid can also use DOT 4 brake fluid.

(Video) DOT 3 Brake Fluid Explained

DOT 4’s minimum boiling point is 450F in dry conditions and 311F in wet conditions. DOT 3, on the other hand, has a minimum boiling point of 400F in dry conditions and 284F in wet conditions.

Understanding the impact of the boiling points of the two brake fluids is crucial because the braking system generates an intense amount of heat between the rotors and the brake pads. If you were to look under the car with a camera, you’d see that the brakes glow red when you press down on the pedal.

This intense heat vaporizes the brake fluid, making it compressible in the process, hence the spongy feel whenever you apply brakes. In the high-performance racing and cars driving in circles, this phenomenon is called the brake fade, and you should avoid it.

Brake fade also comes from the rotor/ brake pad interface where the pads will release gasses, minimizing contact between rotors and the pads. To curb this, the high-end rotors will be drilled and slotted for fast-release of the gases, hence a limitation on the fade.

But, brake fade isn’t limited to racing cars, your car experiences brake fade when you descend a steep hill which is why you need to downshift the gears to a lower gear before a descent. Excess heat could also cause brake fade is you brake too much around corners.

Therefore, the boiling point of the braking fluid is indicative of the temperature at which the vaporization of the brake fluid takes place. And if you will be using the brakes aggressively, always stick to the brake fluid with a high boiling point because it will resist the heat.

Boiling Capacity

The boiling capacity of braking fluid is either dry or wet. The dry boiling point is the boiling point of the brake fluid from a new container, while the wet boiling point is the boiling point of the brake fluid when contaminated with 3.7% of water. The dry boiling point is higher than the wet boiling point.

Keep in mind that all brake fluids except the silicone-based brake fluid, DOT5, are hygroscopic (they absorb water). DOT 3, for example, absorbs as much as 2% water, annually.

Chemical Structure

DOT 3 and DOT 4 braking fluids differ slightly in their chemical structure. DOT 3 is a blend of polyethylene glycol and ether, while DOT 4 is a blend of borate and glycol. The glycol-ether blend is ideal for use in regular vehicles because it holds quite well in hot/ wet conditions; the brakes also heat up easily. DOT 4, on the other hand, has a high water tolerance, as well as stability in high temperatures.

What happens if you mix DOT 3 and DOT 4 brake fluid, Is it OK to mix brake fluid?

Despite the compatibility of DOT 4 with DOT 3 braking fluids, you should not mix the two braking fluids. The braking fluids could react with each other negatively causing the corrosion of the braking system.

Besides reactivity and corrosion, the two brake fluids have different boiling points. And using DOT 3 in DOT 4 braking system could result in the boiling of the brake fluids, hence brake failure. Mixing the two brake fluids is unsafe, and you’re better off sticking to the manufacturer’s recommendations for your vehicle.

Can You Use Dot 3 Brake Fluid In A Motorcycle?

Choosing the right brake fluid for your motorcycle is important as it determines not only your safety, but also the performance and the efficiency of your motorcycle. Therefore, there’s no denying that the brake fluid is a crucial part of the motorcycle’s braking system.

This fluid transfers the hydraulic force applied on the lever into hydraulic pressure, which ensures that the brake system works well. Therefore, it’s important to find and use the right brake fluid.

It’s important to remember the fact that there are many brake fluids on the market and the premium-quality brake fluids are the ones that meet the set standards/ requirements. For example, the brake fluid you buy should follow and meet the standards set by the SAE.

Is motorcycle and automotive brake fluid the same?

Yes, and you can use the automotive brake fluid in your motorcycle’s brake system.

Using DOT 3 Brake Fluid in your motorcycle

The working mechanism of the motorcycle brake system features a motorcycle brake line, which works much like the car brake lines. It delivers the brakes fluid’s pressure to the brakes, from the master cylinder.

Note, however, that unlike the car braking system where the brake’s balance will be handled by the brake’s proportioning valve (the valve determines the amount of the hydraulic pressure on the different axles, hence safety when stopping the vehicle), the brake system of the motorcycles requires you to engage the valves using front and the rear brake controls. You operate the front brake using your right hand, and your left foot operates the rear brake.

The front and the back foot operation will convert the motorcycle’s mechanical force into the brake system’s hydraulic pressure through the lever that acts on the piston pressing the brake fluid.

Can Dot 3 brake fluid be used for power steering?

One of the most expensive mistakes you could make today is to use brake fluid for your steering system.So, if you’re wondering if you can use your unopened DOT 3 brake fluid to power your steering, perhaps because of their lubrication abilities, the answer is NO.

(Video) Can I Mix Brake Fluid DOT Types Together? or With Water? Answers!

Despite the brake and the power steering fluids being hydraulic fluids, they are two different hydraulic fluids with different properties. The two fluids might be lubricants, working well on the seals and the O-Rings, but they don’t function in the same way, chemically.

The power steering fluid refers to an oil/petroleum-based fluid commonly used as a lubricant and pressure transfer medium between different metal-on-metal contacts. This fluid could only be used in dynamic steering where there’s a pump on one side and on the other side, a cylinder.

The brake fluid, on the other hand, refers to the glycol-based fluid (could also be mineral or silicone based) used for static brakes with a cylinder on its primary and secondary side. The brake fluid dissipates heat, it absorbs moisture from the braking system, and though it provides lubrication to the braking system, it’s not the best lubricant. It’s also anti-corrosive, and it optimizes the functioning of the braking system.

What is the difference between brake fluid and power steering fluid?

Besides the definitions and the fact that the braking fluid is essential for the function of the braking system while the power steering is essential for the steering’s function, these two fluids have a number of differences.

For starters, the brake fluid has very low compressibility and a rather high boiling point. On the other hand, the power steering fluid has a high boiling point, highly compressible, and it has a low freezing point.

The two also differ in their applications. The brake fluid is an essential fluid in automobiles, motorcycles, advanced bikes, and light trucks; the power steering fluid is used in power steering, brakes, transmissions, and hydraulic cylinders.

The other difference is that these two fluid power totally different systems – the power steering fluid powers up and optimizes the power of your car’s steering system, while the brake fluid powers your car’s braking system.

The two fluids also differ in the composition of the chemicals they’re made up of.

What happens when you use your DOT 3 brake fluid for the power steering?

Here are some of the things that will happen if you put thebrake fluid in the power steering:

First off, the function of the power steering is affected, and you also have to deal with the bad smell from the brake fluid.

It will further amplify that swelled-up effect on the rubber seals, creating leaks.

It will cost you money getting the brake fluid out of the steering system. And the worst bit is that once the fluid circulates, it becomes even harder to get it out of that system. You should be ready for the long term effects too.

The back and forth movement of the seals/ brake fluid results in the blockage of the passages used by the brake system like the brake-master-cylinder. If the swollen seals block off this master cylinder port, releasing the brake pedal will cause the return of the brake fluid to the reservoir. As this continues to happen, the heat from the braking causes the expansion of the brake fluid. If this expanded fluid fails to make it back to the reservoir, the brakes engage, and the wheels will be locked. The contaminants will further break down the rubber, causing a complete system failure.

What do you need to do if you accidentally add your brake fluid in the power steering?

Let your actions sink in. You’ve created a potentially dangerous situation for your vehicle.

How? The brake fluid could damage your seals, and the rubber seals might swell up, creating more problems. If you don’t resolve this situation first, the brake fluid will dissolve the car’s paint. Therefore, you should act fast!

  • Flush out the brake fluid from the reservoir. This will be easier if you realize your mistake before starting the car. Get your turkey baster and use it to remove the brake fluid from the power steering reservoir. Alternatively, you could detach your running line from the steering located on the primary side of the pump. Do this until the reservoir is empty.
  • It’s more difficult removing the brake fluid after you’ve started the car, but if you’re sure you’ve cleared the reservoir, crank up the engine for a few seconds.
  • Now, with an empty pump, reconnect your system then fill up the reservoir using the right fluid.

Is DOT 3 Brake Fluid Flammable?

DOT 3 Brake Fluid, much like the other brake fluids, is inflammable (flammable) even though it’s non-volatile like the other modern brake fluids,DOT 3 is based on the chemical compound, Polyethylene Glycol (glycol ether).

All the automotive brake fluids known have a significantly high boiling point resulting from the amount of heat generated every time you brake. While you shouldn’t expect the brake fluid to heat up and catch fire while driving, brake fluid is generally a fire hazard. Experiments show that polyethylene glycols ignite when the surfaces they sit in get heated to up 400 degrees Celsius. Therefore, in the event of a collision, the splashing of the brake fluid over an exhaust system heated to about 400 degrees Celsius will result in spontaneous ignition.

While this is not something that happens all the time, the ignition produces a fireball on the exhaust system and the manifold, burning ferociously while spreading to the other plastic components like the air filters and the cable covers.

Is DOT 3 Brake Fluid Ideal for Use in Harleys?

One of the most common questions we come across is “Is DOT 3 Brake Fluid Ideal for Use in Harleys?” Though the answer to this question could be very straightforward given the fact that you can tell the right brake fluid for your motorcycle by reading the master cylinder’s cover, we all know that choosing the right brake fluid for your motorcycle is not that easy. The type of brake fluid you need to use is determined by the Department of Transport (DOT), and the details of the right brake fluid will be stamped on the cover of the master cylinder as DOT 3, 4, or 5. Note that the DOT designation of the brake fluid depends on the fluid’s viscosity and its temperature (boiling) range.

For example, the difference between the DOT 3 and DOT 4 brake fluids lies in their boiling points, and DOT 4 has a higher boiling point than DOT 3. Therefore, DOT 4 brake fluid doesn’t boil as quickly as DOT 3. DOT 5, on the other hand, is silicone-based and very different from DOT 3 and 4. It has a higher boiling point, and it doesn’t absorb as much water as DOT 3 or DOT 4.

Taking these differences into considerations, mixing the brake fluids, or using one in place of the other is not a great idea. Therefore, read the specifications given by the manufacturer and then use or find the fluid recommended. Never mix DOT 5 brake fluid with DOT 4 or DOT 3. You should also avoid mixing brake fluid brands. Unless you perform a brake fluid flush, stick to a brake fluid from one brand because despite having the same name, the fluids might still be incompatible.

(Video) Types of Brake Fluid Discussion With Raybestos Brakes

To protect the components of your Harley and to ensure your safety on the road, the DOT 4 is a recommended brake fluid for your Harley. Therefore, unless yours is an old shovelhead using whose motorcycle’s master cylinder’s cover specifies the use of DOT 5 brake fluid, DOT 4 is your best option.

Is DOT 3 Brake Fluid Synthetic?

DOT 3 is one of the most common brake fluids around, and it’s the ideal pick for standard vehicles or rather, the vehicles that do not require aggressive braking as is the case with racing cars.

Therefore, if you’re looking for brake fluid for your vehicle, it’s highly likely that you’re out for the best of DOT 3 braking fluids. But with numerous brands some named synthetic and many other donning tags like conventional or regular, which one should you choose?

Well, if you’re confused by the tags, wondering if DOT 3 brake fluid is synthetic, here the simple answer you’ve been looking for –Yes, DOT 3 is synthetic

DOT 4 and DOT 5.1 are also synthetic. The only brake fluid that’s different from the rest is DOT 5 which is a silicone brake fluid. While mixing brake fluids is ill-recommended, you should know that only DOT 3, 4, and 5.1are compatible, chemically. But, never mix two types of brake fluids.

Benefits of Synthetic Brake Fluid

Are you feeling confused by the different terms used to describe the brake fluids? This section aims to clear the air for you.

The primary component of the brake fluid is a base oil. The fluid also contains additives, but the base oil is the most important component of the brake fluid. The reason for this is that the base oils are created differently, and they fall into five main categories or groups I-v. Out of the five groups, group III and Group IV base oils are the only ones that are 100% synthetic. Group II base oils are also high-quality oils and are, therefore, acceptable as synthetic or oils with a synthetic-like performance. On the other hand, Group I and II base oils are regarded as mineral-based.

It’s also worth mentioning that the synthetic oils, get their high ranking from their low volatility which results in low oil consumption, and the high oxidation stability which results in the lengthening of the oil’s life.

Esters, like the DOT 3 brake engine uses the Group V base oils – these are the oils absent in the Groups I –IV.

The full synthetic base oils could be easily engineered in the laboratory to cater for different applications because of their purity and high-quality, as well as the high viscosity index that stops the oils (in this case the brake fluid) from becoming too cold or too thin. The full synthetics include the brake fluid esters, and they boast high heat resistance, as well as top performance.

Therefore, you should use the synthetic DOT 3 brake fluid rather than the mineral-based ones. The latter has a low viscosity, they are impure, and they don’t provide the necessary protection needed by the brake system.

Audi A6 Brake Fluid Top Up

Can you tell when your Audi A6 needs a brake fluid top up without taking your car to the mechanic or calling your car-guy friend. You should. Failure to top up your car’s brake fluid on time could risk damage to the braking system and the rest of the car’s internal transmission systems. In this article you will learn about the signs of an Audi A6 that needs a top up of the brake fluid, as well as the top up process. For starters, the hint lies in the lights. If the car’s brake warning lights or its ABS light indicator is on, then it means that it’s time for a brake fluid top up.

How to Top up Your Audi A6 Brake Fluid

  • Before we look at how to replenish your vehicle’s lifeblood, how about we look at some of the things that signal the need for a brake fluid top up, besides the warming ABS lights?
  • Softness or mushiness of the brake pedal
  • You can press your brake pedal, all the way down or too close to the floor. In either case, this is a symptom of low brake fluid levels.
  • Pumping: if you have to press your brake pedal at least twice to bring your car to a complete stop, check the brake fluid levels and top up
  • If you have the low brake fluid warning on the dashboard, or if you see a brake fluid leak under the car, get the brake system checked. Note that the brake fluid can be brown or clear.

When do you need to top up your Audi A6 brake fluid?

In most cases, the manufacturer recommends the times for the brake fluid change or even brake fluid flushes. Generally, this recommendation is between 20,000 miles and 100,000/ 150,000 miles. If you’re unsure of how to fix the brake fluid problem, seek help from your nearest Audi technician.


Despite DOT 3’s recommendation as the best brake fluid for passenger vehicles and small vehicles, note that the fluid will not last forever and you need to replace the fluid as recommended. Being hygroscopic, excess moisture accumulation results in the corrosion of the brake system, which could leave you with a spongy pedal or worse issues like vapor lock.


Are All DOT 3 Brake Fluids the Same?

In the world of new innovations there is a mindboggling number of brake fluids, and your search for the best product might not be as easy. But despite the confusing brand names and components, you cannot afford to make a mistake of buying the wrong brake fluid. Look at DOT 3 brake fluid, for example, there are many varieties/ brands of this brake fluid, but it’s fascinating to note that two DOT 3 brake fluids are hardly ever exactly the same. So, regular or synthetic, you’ll find yourself dealing with one kind of product, unless you find glaring differences in the ingredients/ active components. DOT 3 brake fluid is notably the most common brake fluid used in the older vehicles and some of the new vehicles. DOT 3 brake fluid represents a glycol-based (glycol-ether) braking fluid that works well in older and most of the regular passenger vehicles.

How much does it cost to flush braking fluid?

Braking fluid in itself is relatively inexpensive and therefore the labor costs are also reasonable. If you plan on doing it expect to spend between $70 to $100. This will depend on your type of car and the process is very straightforward.

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