When it comes to the safety of your vehicle, the braking system plays a crucial role. And at the heart of every braking system is the brake fluid. Choosing the right brake fluid for your vehicle is essential for optimal performance and safety.
It performs the critical task of transferring pressure from the brake lever to the brake pads and must consequently be non-compressible. The ideal brake fluid will have a high boiling point and should also be able to lubricate calipers and resist corrosion.
Currently, four types of braking fluid are available in the market: DOT 3, DOT 4, DOT 5.1, and DOT 5. The type chosen by drivers depends on the style of their vehicle or racing performance specifications.
As kinetic energy is converted to heat by brakes, a significant amount of heat is subjected upon the fluids, which requires them to handle more heat before reaching their boiling point.
Regarding viscosity, Dot 3 and 4 remain steady at temperatures up to 149°C (300°F). However, Dot 5 stands out with its larger transfer capability at 350°F (177°C). On the other hand, Dot 5.1 offers superior thermal stability compared to other fluids at 400°F (204°C).
Each braking fluid provides unique features for different driving applications, making it essential for drivers to make a wise selection among them when making their choice. Read on to learn more in detail about it.
What is brake fluid?
Brake fluid is a hydraulic fluid utilized by the braking system in your ride. Upon pressing the brake pedal, the brake fluid pushes the pistons in the caliper to grip the brake rotors, the reason why your car pulls to a stop or reduces speed when applying brake pedal pressure.
In effect, the brake fluid transfers the force applied to the brake pedal to the brake calipers. And since the brakes are operating in a high-friction and high-stress environment, the brake fluid needs to perform flawlessly at extreme temperatures and high-pressure scenarios.
Furthermore, the brake fluid lubricates the rubber and metal components in the calipers and master cylinder to prevent rust and corrosion.
How Brake Fluid Works?
Brake fluid is a hydraulic fluid that is used in the braking system of a vehicle. It helps to transfer the force from the brake pedal to the brakes, allowing them to slow down or stop the car.
The brake fluid also helps to keep the brakes lubricated and prevents corrosion of metal parts.
Brake fluid works by transferring pressure from the brake pedal through a series of tubes and hoses to the brakes.
When the brake pedal is pressed, it causes a plunger to move inside the master cylinder, which then pushes the brake fluid through the system. The pressure of the fluid is then transferred to the brakes, causing them to slow down or stop.
The type of brake fluid used in a vehicle depends on its make and model. Different types of brake fluids have different boiling points and viscosity levels, which can affect the performance of the brakes. The most common types are DOT 3 and DOT 4 brake fluids.
DOT 3 brake fluid is a glycol-based fluid that has a low boiling point and is suitable for most vehicles. It is also compatible with water, which helps to reduce the corrosion of metal parts in the braking system.
DOT 4 brake fluid is a borate ester-based fluid that has a higher boiling point than DOT 3 and is more resistant to water.
This makes it ideal for high-performance vehicles that require a higher boiling point. It is also more resistant to corrosion, making it a better choice for vehicles that are exposed to extreme temperatures or moisture.
DOT Brake Fluid Explained
The most commonly used brake fluid today is DOT fluid. All the DOT fluids apart from the DOT 5 are made of the poly-glycol base.
Glycol-based brake fluids are a mixture of as many as ten ingredients, making the final products. The substances can be broken into four major components, which include:
- Inhibitors: They prevent oxidation and corrosion.
- A Modifier Coupler: This changes the number or intensity of swelling on the exposed rubber parts.
- A Solvent Diluent: It determines the viscosity and boiling point of the brake fluid. It accounts for 50% to 80% of the brake fluid. The commonly used solvent diluent is a glycol ether.
- A Lubricant: Lubricants such as polypropylene or polythene keeps the parts moving freely from 20% to 40%.
DOT brake fluid meets stringent specifications and standards set by the Department of Transportation and the Society of Automotive Engineers. DOT gets its name from the Department of Transportation.
The standards focus on maintaining the performance of brake fluids in both low and high temperatures. They also give specifications on the minimum boiling temperatures to which the manufacturers of the fluid should adhere.
There are different types of DOT brake fluids. The DOT brake fluid types include DOT 5.1, DOT 5, DOT 4, DOT 3, and DOT 2 brake fluid. The main thing that separates the various classes of DOT brake fluids is their boiling points or temperatures.
Boiling points refer to where the brake fluid will begin to boil or vaporize in the brake system. It is mainly caused by heavy and prolonged brake use, which has an adverse effect on the performance of the whole brake system.
Brake Fluid Types and Applications
Glycol-Based Brake Fluids
DOT 3 uses glycol ether as a solvent. This conventional brake fluid was used in vehicles produced up until the 1990s and remains suitable for all brake systems and all driving conditions.
DOT 4 combines glycol ether and borate ester compounds, delivering superior performance compared to DOT 3. Vehicles produced after 2006 use DOT as their standard brake fluid. It is suitable for all brake systems and driving conditions.
DOT 5.1 incorporates glycol ether and borate ester compounds with enhanced performance capabilities similar to silicon-based DOT 5 but is compatible with DOT 3 and DOT 4 types of braking systems and fluids.
All glycol-based brake fluids should be handled carefully. They can damage vehicle paint.
Silicone-Based Brake Fluid
DOT 5 is a silicone-based fluid that makes it incompatible with anti-lock braking systems. It cannot be mixed with other brake fluid types. Unlike glycol-based fluids DOT 5 does not damage paintwork.
This fluid is engineered for demanding applications like military vehicles and extremely cold climates.
What Are Brake Fluid Major Features?
The braking system is a mechanism with extreme operating temperatures. That is why the brake fluid needs to possess certain features to be able to meet those conditions. Moreover, its major features include:
- Non-compressibility – For effective force transfer
- Low viscosity – For compatibility with ABS
- Lubricity – For lubricating the sealings
- Corrosion resistance – For protecting braking system components
- High boiling point – For resisting high temperatures and not vaporizing, which would affect the transfer of the braking force.
What is DOT 3 Fluid?
DOT 3 brake fluid is a petroleum/non-mineral based, non-silicone, totally synthetic brake fluid used in various clutch and braking applications. It is formulated with alcohol and glycerin and utilizes polyethylene glycol ether for its high-performance properties.
The boiling point of the brake fluid ranges from 205° C (dry) to 140° C (wet). This wide range guarantees a reliable and safe braking experience even at high temperatures and helps combat fluid boiling or thickening in hot or cold conditions.
DOT 3 fluids can conveniently handle temperatures much higher than normal braking environments – making them ideal brake fluids for vehicles subjected to extreme weather conditions or sustained heavy use.
Furthermore, proper maintenance, such as changing the full fluid after two years or 30,000 miles, should be followed to ensure optimal results.
Always check your vehicle’s manual to determine what type of DOT rating you should use in different parts of the vehicle system.
What is DOT 4 Brake Fluid?
DOT 4 brake fluid is a glycol ether-based and borate ester-boosted system that offers superior wet and dry boiling points than its predecessor, DOT 3.
Most vehicles now have DOT 4 installed in their systems by default, as the long-term performance benefits of these fluids are far better. For example, the dry boiling point on this type of brake fluid is set at 230°C while the wet boiling point is 155°C.
This means it has greater resistance to overheating after extensive use and when submerged underwater; however, the extent of this benefit may vary in some instances, so it’s advisable to consult the automobile manufacturer before inserting DOT 4 in your vehicle’s braking system.
Additionally, not every bike or car requires DOT 4 brake fluid to work correctly, so it is best to check before using this type of fluid.
What is DOT 5 Brake Fluid?
DOT 5 brake fluid is becoming increasingly popular in the automotive industry due to its superior high boiling points.
This feature makes it more costly than other options, but motorists willing to invest the money will be met with greater safety and performance benefits.
It boils at 260° C dry and 180° C wet, which should provide ample protection under most circumstances.
The fact that DOT 5 does not mix with water also means that drivers do not need to worry about corrosion as much when using this type of fluid for their vehicle’s brakes.
Modern vehicles’ thin, compact rotors benefit from DOT 5 since the silicon-based fluid can better handle the higher temperatures resulting from good heat dissipation.
In addition, the braking response should remain consistent even when on extended drives or under harsh conditions.
Regardless, drivers should check their brakes regularly and stick within their vehicle’s specified brake fluid maintenance intervals to ensure they stay safe while on the road.
What is DOT 5.1 Brake Fluid?
DOT 5.1 is a unique brake fluid that has gained popularity due to its superior performance compared to other DOT fluids and its ability to withstand higher temperatures without becoming sticky.
It combines a borate ester and polyethylene glycol ether and performs better than any other DOT brake fluid on the market.
It has an impressive dry boiling temperature of 270° C and 190° C wet, making it one of the best options for vehicles requiring great braking capabilities.
Another advantage of using this type of brake fluid is its compatibility with all glycol-based fluids. While this does not include DOT 5 because it is silicone-based, you should not worry about mixing different brakes when working on your vehicle.
Dot 5.1 also offers excellent longevity, meaning you don’t have to replace it often to maintain optimal braking performance. Because of this, many drivers opt for this type of fluid as they know they can count on its reliability over time.
Pros And Cons Of DOT 3, DOT 4, DOT 5, And DOT 5.1 Brake Fluid
DOT 3
Pros
- DOT 3 brake fluid is cheap and available at low prices
Cons
- Outdated brake fluid
- Has the lowest boiling point among all the other brake fluids
- Low durability
DOT 4
Pros
- Most compatible brake fluid for motorcycles
- Higher boiling points and better lifespan than DOT 3
- Affordable and low cost
Cons
- Hygroscopic – absorbs moisture easily
- Still, lower boiling points and lifespan when compared to DOT 5 and DOT 5.1
DOT 5
Pros
- Do not absorb moisture
- Higher boiling point
- Harmless to painted surfaces
Cons
- Expensive
- Not suitable for motorcycles and other vehicles
- Limited application
DOT 5.1
Pros
- Higher boiling points
- Less hygroscopic than DOT 3 and DOT 4
Cons
- Expensive
- Low compatibility since most vehicles are designed for DOT 4
DOT 3 vs. DOT 4 Brake Fluid: Which One Is The Better Brake Fluid?
DOT 3 brake fluid is a more popular type of brake fluid for cars and trucks. It is low-cost and a standard option for average cars where the driver is not likely to engage in vigorous braking actions.
DOT 4 is also gaining popularity due to its compatibility with traction control and anti-lock braking systems. It is ideal for police and racing cars that need vigorous braking to use mush regularly.
Below are some other differences between the DOT 3 and DOT 4:
#1. Chemical Structure.
The chemical components in DOT 3 vs. DOT 4 have a slight difference. DOT 3 is made by blending polyalkylene and ether, while DOT 4 is a mixture of borate and glycol.
The glycol ether holds quite well in wet and hot conditions, which makes it a perfect choice for regular vehicles. DOT 4, on the other hand, has a high tolerance to water and is stable under high temperatures.
#2. Boiling Point.
The major difference between DOT 3 and DOT 4 fluids is their boiling points. DOT 3 has a lower boiling point, and thus it assimilates water more easily. It, therefore, boils faster when put under rough and hard braking, and this could damage the braking systems.
DOT 4 has a higher boiling point. It is an alternative to DOT 3 brake fluid, but the latter cannot be used in place of the former.
#3. Boiling Capacity.
DOT 3 brake fluid has a great dry and wet boiling capacity. It means that it will still work better when exposed to open air and water compared to DOT 4.
DOT 4 braking fluid, on the other hand, has a better dry boiling capacity, but its wet boiling capacity is not very good.
Differences Between DOT 4 and DOT 5 Brake Fluid Grades
Let’s explore the key differences between DOT4 and DOT5 oil grades for brake fluid.
- Composition
- Hygroscopic vs. Hydrophobic
- Boiling points
- Compatibility
- Vehicle Applications
- Fluid color
- Compressibility
- Shelf life
- Handling requirements
- Pricing
#1. Composition.
To understand the differences between the composition of DOT 4 and DOT 5 grades for brake fluid, you need to know their distinct properties and ingredients.
DOT 4 brake oil is glycol-based and contains a mixture of glycols, borate esters, and other additives. These components provide DOT 4 with excellent anti-corrosion properties and low viscosity, making it suitable for most standard brake systems.
Alternatively, DOT 5 brake oil is silicone-based, featuring silicone polymers as its primary ingredient. This composition offers increased resistance to moisture absorption, making it a preferred choice for specialized applications.
#2. Hygroscopic vs. Hydrophobic.
DOT 4 brake fluid is hygroscopic, which tends to absorb atmospheric moisture over time. This moisture absorption can lead to a reduction in its boiling point and can cause degradation of the brake system.
On the other hand, DOT 5 fluid is hydrophobic, which means it repels water and doesn’t absorb moisture. This hydrophobic property allows DOT 5 brake fluid to maintain a stable boiling point and resist performance degradation caused by moisture.
#3. Boiling Points.
Understanding the boiling points of these two oil grades is essential because it directly affects the performance and safety of your braking system.
DOT 4 brake fluid has a dry boiling point of around 230°C (446°F) and a wet boiling point of approximately 155°C (311°F).
Conversely, DOT 5 brake fluid boasts a higher dry boiling point of around 260°C (500°F) and a wet boiling point of roughly 180°C (356°F). These higher boiling points make DOT 5 brake fluid more suitable for extreme temperatures and high-performance conditions.
#4. Compatibility.
DOT 4 brake fluid is compatible with most standard braking systems, including anti-lock braking systems (ABS). This makes it a suitable choice for passenger vehicles. However, DOT 4 brake fluid isn’t typically compatible with silicone-based DOT 5 brake fluid.
On the other hand, DOT 5 brake fluid is less compatible with standard brake systems and shouldn’t be used in vehicles with ABS. Mixing DOT 5 with glycol-based brake fluids like DOT 3 or DOT 4 can lead to system malfunctions.
#5. Vehicle Applications.
To understand the differences in vehicle applications between DOT 4 and 5 brake fluid grades, consider their specific properties and how they impact performance and safety.
DOT 4 brake fluid is widely used in various vehicles, such as passenger cars, trucks, and motorcycles, and is suitable for everyday driving conditions. It provides excellent performance and meets the requirements of most vehicles on the road.
On the other hand, DOT5 brake fluid isn’t as versatile and is typically used in specialized applications. It’s often specified for high-performance vehicles, certain military vehicles.
#6. Fluid Color.
DOT 4 brake fluid is typically clear to amber in color, allowing easy visual identification. This is particularly useful when checking the fluid level in the master cylinder.
As opposed to this, DOT 5 brake fluid is usually purple in color. This distinct color serves as a visual marker, helping to prevent accidental mixing with glycol-based fluids.
By having a different color, DOT 5 brake fluid ensures that it’s easily distinguishable from other types of brake fluids.
#7. Compressibility.
When comparing DOT 4 and DOT 5 brake fluid grades, you’ll notice a significant difference in compressibility.
DOT 4 brake fluid, being less compressible, can transmit hydraulic pressure more efficiently. This results in a more responsive braking experience with a firm, solid pedal feel.
Then again, DOT5 brake fluid is more compressible than DOT 4 glycol-based fluids. This characteristic leads to a slightly softer pedal feel. While some drivers may prefer the softer pedal feel of DOT 5 fluid, it’s worth considering the trade-off in terms of responsiveness.
The more compressible nature of DOT 5 fluid may result in a slightly longer pedal travel and a potentially delayed response in braking.
#8. Shelf Life.
DOT 4 brake fluid, once opened, has a relatively short shelf life of around one year. After this period, it may start to absorb moisture, leading to a decrease in its effectiveness.
However, DOT 5 brake fluid has a longer shelf life once the container is opened. It can last up to three years before significant moisture absorption occurs. This extended shelf life can be advantageous for vehicles that aren’t frequently used.
#9. Handling Requirements.
DOT 4, a glycol-based brake fluid, is more forgiving when handling and spillage. It’s less likely to cause damage to vehicle paint or surfaces in the event of a spill.
On the other hand, DOT 5, which is silicone-based, can be more challenging to handle. It tends to damage paint and surfaces, making care and precaution necessary during maintenance.
#10. Pricing.
Regarding cost, DOT 4 brake fluid offers a more budget-friendly option than DOT 5. This affordability is particularly beneficial for routine maintenance, where cost-effectiveness is a significant consideration.
In contrast, DOT 5 brake fluid tends to be pricier than glycol-based alternatives. The higher cost can be attributed to the specialized nature of DOT 5, which offers advantages in terms of longevity and performance.
Can We Mix Brake Fluids?
Yes, but with certain exceptions. Brake fluids can be mixed only if the fluid that you add to the system belongs to a higher grade.
For example, a braking system that has a brake fluid DOT 3 specification can use a DOT 4 or a DOT 5.1 fluid. Also, a system with a DOT 4 can be topped up with a DOT 5.1 without bleeding the system.
However, never top up a DOT 4 system with a DOT 3 brake fluid. DOT 3 won’t be able to meet the temperature requirements because of its lower dry and wet boiling points.
Once again, do not mix DOT 5 with any other type of brake fluid because of its silicone-based composition.
For optimal braking system and brake fluid performance, it is best to bleed the brake fluid and replace it with a fresh one.
How Is Brake Fluid Rated?
Brake fluid ratings are based on the fluid’s boiling point. Two types of measurements are used to rate brake fluid. The dry boiling point is for pure brake fluid, whereas the wet boiling point measures water-contaminated fluid.
The Department of Transportation (DOT) defines the ratings for all brake fluid types, including DOT 3, DOT 4, DOT 5, and DOT 5.1.
By referring to the table below, the ratings for each type are identified. As you can see in the table, the composition of each type corresponds to the wet and dry boiling point.
In many cases, the type of fluid used in a vehicle is determined by the potential for higher temperatures based on speed and heavier towing loads. In comparing DOT 3 vs DOT 4, the boiling point and lifespan are the critical variables.
Typically, DOT 4 fluid will need to be replaced more often as it absorbs moisture faster than DOT 3 fluid. The DOT 5 and DOT 5.1 brake fluids are not compatible with Antilock Braking Systems (ABS), so as a result, they are used less often than DOT 3 and DOT 4.
Due to the different rating characteristics of each fluid, it is important to never mix them and only use brake fluid that conforms to your vehicle manufacturer’s recommendation. If unsure, check your owner’s manual or bring your vehicle to a service center.
The ratings are developed in regard to your brake fluid’s boiling point.
| Characteristic | DOT 3 | DOT 4 | DOT 5 | DOT 5.1 |
| Dry Boiling Point | 401°F | 446°F | 500°F | 500°F |
| Wet Boiling Point | 284°F | 311°F | 356°F | 356°F |
| Composition | 80% Glycol Ether base | 50-65% Glycol Ether, 20-30% Borate Ester | Silicone-based | 20-30% Glycol Ether, 50-70% Borate Ester |
| Moisture Absorption Rate | Slower than DOT 4 | Absorbs moisture 20% faster than DOT 3 | Does not absorb moisture (non-hygroscopic) | Similar to DOT 4, but less moisture absorption over time |
| Typical Use | Older vehicles, lighter use | Modern vehicles, heavier loads, towing | Specialized uses like classic cars, military vehicles | High-performance vehicles, compatible with DOT 3 & DOT 4 |
| Replacement Frequency | Less frequent | More frequent | Less frequent, since it doesn’t absorb water | Regular, due to higher performance needs |
| Compatibility | Compatible with DOT 4 and DOT 5.1 | Compatible with DOT 3 and DOT 5.1 | Not compatible with DOT 3, DOT 4, or ABS brakes | Compatible with DOT 3 and DOT 4 |
Difference between DOT 3, DOT 4, and DOT 5 Brake Fluids
| Options | DOT 3 | DOT 4 | DOT 5 |
| Boiling point | Dry: 401 F/205 CWet: 284 F/140 C | Dry: 446 F/230 CWet: 311 F/155 C | Dry: 500 F/260 CWet: 356 F/180 C |
| Chemical structure | It is made by mixing ether and polyalkyelen glycol. | It is a mixture of borate and glycol. | It is made by blending hydrophobic.Polydimethylsiloxane and Tributylphosphate. |
| Boiling capacity | It has a great wet and dry boiling capacity. | Its dry boiling capacity is great, but the wet boiling capacity is not so good. | It has the best dry and wet boiling capacity. |
| Colors | Colorless to amber | Colorless to amber | Purple |
| Meets Requirements of | FMVSS 116,SAE J1703ISO 4925 Class 3 | FMVSS 116,SAE J1704ISO 4925, Class 4 | FMVSS 116,SAE J 1705ISO 4925, Class 5 |
| Price | Its price ranges from $13 to $16. | It costs between $15 and $19. | The price is between $18 and $45. |
FAQs.
Q: What Happens If You Mix DOT 3 And DOT 4?
Mixing DOT 3 and DOT 4 will give you an unpredictable boiling performance, which should not cause any harm. These brake fluids are compatible with one another, and thus, there is no problem in mixing them.
The difference between the two is minimal. However, professionally, I would advise you to use one or the other instead of mixing.
Q: When Should I Use DOT 4 Brake Fluid?
You can use DOT 4 brake fluid if you want to upgrade from DOT 3. DOT 4 has a high boiling point, and thus it is ideal for cars that engage in vigorous break actions, like motorcycles, racing cars, and police vehicles.
It is also compatible with cars using anti-lock braking systems. It is advisable to use the DOT 4 brake fluid if the car manufacturer suggests so.
Q: Are All DOT 4 Brake Fluids The Same?
All DOT 4 fluids are synthetic brake fluids, and their chemical composition is the same. All DOT 4 brake fluids have the same wet and dry boiling points, and thus, you can use any, depending on your preference. They are a blend of borate ester and glycol.
Q: Does DOT 5 Absorb Water?
DOT 5 does not absorb water, causing it have a high boiling point. Since it is silicone-based, it does not allow moisture to get into the brake system.
If any moisture gets in the brake system, it collects itself in pockets, which later boils off or freezes. The moisture leads to the failure or damage of the brake system.
Conclusion
Brake fluid is mandatory for every type of vehicle. It does not matter if you are driving an economy car, truck, or motorcycle. The work of the brake fluid is to move the vital components of the braking system easily.
The brake fluid enables the pistons to compress the rotors on the braking system so that the car can slow down.
There are various brake fluid types just like we have seen in the above DOT 3 vs. DOT 4 article.
The type of brake fluid you choose will depend on the type of brake system you are using. Most vehicle manufacturers will also recommend for you the brake fluid you should use.
It is very important to follow the recommendations given by your car manufacturer in the manual. You can upgrade from DOT 3 to DOT 4 to DOT 5.1.
These brake fluids are glycol-based. DOT 5 brake fluids are silicone-based, and you should not mix them with other fluids. This brake fluid was mainly made for military vehicles. Ensure that you use the right type of brake fluid for your vehicle to maintain safety.