What is The Difference between DOT 3, DOT 4 and DOT 5 Brake Fluids

Brake fluids are responsible for transmitting pressure from the brake lever to the brake pads. These fluids need to be non-compressible for them to transfer the force effectively. The best brake fluid should be able to lubricate the calipers, offer resistance to corrosion, and have a high boiling point. Brake fluid comes in four types. There are DOT 3, DOT 4, DOT 5.1, and DOT 5 brake fluids.  Brake fluids are subjected to an average amount of heat since brakes convert kinetic energy to heat.

However, it can only withstand a certain amount of heat before it starts to boil. When it boils, it will form air bubbles, and this will make it compressible, which will affect how the braking system works. DOT 3 and DOT 4 are the most common brake fluids used in automobiles. This comparison between the DOT 3 vs. DOT 4 brake fluids will help you to make the right decision on the one to use on your vehicle.

Meaning Of DOT Brake Fluid

The most commonly used brake fluid today is the DOT fluid. All the DOT fluids apart from the DOT 5 brake fluid 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:

  1. Inhibitors- They prevent oxidation and corrosion.
  2. A Modifier-Coupler- This changes the number or intensity of swelling on the exposed rubber parts.
  3. 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.
  4. A Lubricant-Lubricant such as polypropylene or polythene keeps the parts moving freely for 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 which the manufacturers of the fluid should adhere to.

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.

DOT 3, 4, 5, and 5.1 Explained YouTube Video

What is DOT 3 Fluid?

DOT 3 brake fluids are a petroleum/non-mineral based, non-silicone, and fully synthetic brake fluid designed for use in a wide range of clutch and brake applications. It is made by mixing alcohol and glycerin. The brake fluid is based on polyethylene glycol ether technology for high performance.

The main advantage of DOT 3 brake fluid is that it has high boiling points that provide a safe and consistent performance when the braking pressure is high. This brake fluid is designed to withstand high temperatures without boiling and cold temperatures without thickening. DOT 3 brake fluids can withstand high temperatures of up to 250° C.

The rubber component swell in DOT 3 brake fluid is minimal, thus reducing the loss of fluid and leakages. It also has excellent corrosion protection, which improves the reliability and life of the components in the brake system.

This brake fluid is suitable for top-up or re-fills of clutch and brake systems in heavy-duty commercial vehicles, motorcycles, and 4WD’s and passenger cars. You can also use it on agricultural, construction and mining equipment.

Use this brake fluid when the vehicle manufacturer specifies to use DOT 3 brake fluid. The fluid is naturally hygroscopic and absorbs water from the air, which lowers the effectiveness of the product. Once you open the brake fluid bottle, make sure you reseal the cap tightly to prevent it from getting contaminated with water.

You should change the brake fluid based on the service specifications given by the manufacturer. You are advised not to mix the DOT 3 brake fluid with Mineral or Silicone DOT 5. Always wear protective gear when using the brake fluid to prevent contact with paint, varnish, or skin.  In case your skin gets into contact with the brake fluid, wash it with water immediately.

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What is DOT 4 Brake Fluid?

DOT 4 brake fluids are glycol ether-based and have an addition of borate esters, which improves its performance. Some of the things that the borate esters improve are the wet and dry boiling points. DOT 4 brake fluid has a higher and stable boiling point compared to the DOT 3. However, when it begins to absorb water, the boiling point falls more rapidly than the DOT 3 brake fluid.

DOT 4 should have a minimum wet boiling point of 155°C and a minimum dry boiling point of 230°according to the set standards. Use the DOT 4 brake system only if it is a preference for your brake system or if the car manufacturer has specified so. You are advised not to use this brake fluid for lower or upper-grade vehicles.

It is recommended to change the DOT 4 brake system every two years to maintain the maximum safety and performance of the brake system. The lifetime of the brake system reduces when water contaminates it. DOT 4 brake fluid absorbs moisture through the brake hoses. The brake fluid heats up as you continue to use the brake system.

The boiling point of the brake fluids will decrease as they continue to absorb water from the air. If you fail to change brake fluids regularly, the wheel cylinders and master cylinders rubber parts will start corroding. You can mix DOT 4 with DOT 3 and DOT 5.1 without reducing performance or causing damages to the braking system since they are glycol-based.

However, even if it is safe to mix them, professionally, I would not advise you to combine them. DOT 4 is an alternative of DOT 3 but not the other way round. Make sure that you have flushed out all the brake fluid from the brake system before you fill the reservoir with another type of brake fluid. This brake fluid can withstand temperatures as much as 311 degrees.  DOT 4 has a viscosity of 1800 at 40 F.

What is DOT 5 Brake Fluid?

DOT 5 brake fluids are silicon fluid, and it is used in most modern cars. It is more expensive compared to others since it has a high bylining point. It has a dry boiling temperature of 356 degrees. Most of the new brake rotors are thin and small, and thus they disperse a lot of heat. This silicon-based brake fluid is ideal for this type of car since it can withstand high temperatures.

A DOT 5 brake fluid does not absorb moisture, and it does not cause any harm to painted surfaces. This brake fluid acts as a weather barrier to the brake system. DOT 5 can replace DOT 3 and DOT 4, but you should not mix it with any of the other brake fluid. Silicon-based brake systems are more difficult to bleed.

However, once they bleed, a brake system filled with DOT 5 brake fluid will resist rust better and also stay for a longer period than other formulations. This brake fluid is also lighter in cold temperatures. It weighs around 900 at 40 F. The viscosity of DOT 5 is much more stable in extreme temperatures. It is ideal can be used in most external boots, and it is also compatible with all components of standard brakes.

DOT 5 brake fluids also have some drawbacks. It expands significantly when hot and the additives can vaporize at moderate temperatures, thus increasing the spongy feel. This fluid is incompatible with systems that have used glycol-based fluids before unless you flash it and have the seal replaced. It is also not compatible with anti-lock brakes wince the silicone fluids are more viscous. Unlike glycol fluids that start compressing when they near their boiling points, silicone brake fluids begin to compress when it gets to 300-350 degrees Fahrenheit.

What is DOT 5.1 Brake Fluid?

Most people think that DOT 5.1 is a modification of DOT 5, but that is not the case. DOT 5.1 is silicone-based, and it is a combination of borate ester and polyalkylene glycol ether. DOT 5.1 brake fluid sustains more heat than other DOT brake fluids without any mushy feelings. It can withstand higher dry and wet boiling temperatures and provides superior performance over all the other DOT brake fluids.  You can mix it with all the glycol-based brake fluids, but it is not compatible with DOT 5.

This fluid has a dry boiling temperature of around 275 Degrees Celsius, which is higher than that of a racing fluid. Another advantage of DOT 5.1 is that it is convertible with rubber formulations. It is also congenial with DOT 3 and DOT 4. It is, therefore, easy to make an upgrade from the other DOT 3 and DOT 4.

On the downside, DOT 5.1 will absorb water, it eats paints, and it is also expensive than DOT 3 and DOT 4. This brake fluid is also challenging to find it is some auto parts stores. The brake fluid is not compatible with DOT 5, and you should never mix it for whichever reason.

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 vs. DOT 4:

01.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 I wet and hot conditions, which makes it a perfect choice for regular vehicles. DOT 4, on the other hand, has a high tolerance of water and its stable under high temperatures.

02.Boiling Point

The major difference between DOT 3 vs. 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 of DOT 3 brake fluid, but the latter cannot be used in place of the former.

03.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.

Difference between DOT 3, DOT 4 and DOT 5 Brake Fluids

OptionsDOT 3DOT 4DOT 5
Boiling point

 

Dry: 401 F/205 C

Wet: 284 F/140 C

Dry: 446 F/230 C

Wet: 311 F/155 C

Dry: 500 F/260 C

Wet: 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.
ColorsColorless to amberColorless to amberPurple
Meets Requirements ofFMVSS 116,

SAE J1703

ISO 4925 Class 3

FMVSS 116,

SAE J1704

ISO 4925, Class 4

FMVSS 116,

SAE J 1705

ISO 4925, Class 5

PriceIts price ranges from $13 to $16.It cost between $15 and $19.The price is between $18 and $45.

FAQ

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. Their difference between the two is minimal. However, professionally, I would advise you to use one or the other instead of mixing.

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.

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.

Does DOT 5 Absorb Water?

DOT 5 has does not absorb water, and this makes it have a high boiling point. Since it is silicone-based, it does not allow moisture to get in 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.

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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 it 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.

Tito

Hi There, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanics (Both Heavy Commercial and Private Cars). I have been working as a mechanic for over fifteen years. I worked for a long time at Global Rebound Automotive companies (Toyota, TATA, BMW, Nissan, TVs, and Others ) as a Mechanic and Mechanics Supervisor.

2 thoughts on “What is The Difference between DOT 3, DOT 4 and DOT 5 Brake Fluids

  1. Hi Tito,
    My name is Vincent, and I’m presently thinking of converting the drum brakes on my 1967 Pontiac from front drum to disc brakes. I should mention that I’ve had the engine upgraded a bit, and it’s now pushing around 500 HP, and I already had a mild suspension upgrade done as well. Should I upgrade to DOT 4 when I have the conversion done, or stay with the DOT 3? The reason I ask is I’m not sure which is better for a semi-restomodded classic car that isn’t trailered around, but also not driven daily – I take it out a couple times a week for around 50-200 miles, depending on what I’m doing with it (shows, meets or just fun trips), and usually once a year I take it a longer trip, which can be up to 1500 miles. In any case I’m assuming you probably don’t take questions through this site, which I can understand. If you have a general answer that you could add to the info above that would also be more than enough for me – Thanks in advance!

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