Can I Use DOT 4 Instead Of DOT 3 Brake Fluid | Differences

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When it comes to your vehicle’s scheduled maintenance, a common question you will come across when filling brake fluid is whether you can use DOT 4 instead of DOT 3 brake fluid.

On the market, we can find mainly four types of brake fluid. Many modern cars and trucks commonly use DOT 3 and DOT 4 brake fluids, and these two fluids have similarities and differences. The U.S. Department of Transportation (DOT) introduced this classification based on product specifications.

This article covers DOT 4 and DOT 3 brake fluid differences and can use DOT4 instead of DOT 3.

Adding brake fluid DOT 3 vs DOT 4
Brake fluid DOT 3 vs DOT 4.

Dot 3 vs. Dot 4 Brake Fluid Differences.

Boling Point: DOT 3 and DOT 4 brake fluids have similar properties, but they have several differences. The significant difference between DOT 3 vs DOT 4 is composition and boiling point, and DOT 3 has a dry boiling point of 401F (205C) and a wet boiling point of 284°F (140°C), and DOT 4 has a dry boiling point of 446°F (230°C) and a wet boiling point of 311°F (155°C).

Chemical structure: DOT 3 fluid is made of polyethylene and Glycol Ether, and DOT 4 is made of Glycol Ether and Borate Ester.

Water contamination: These two braking fluids are hygroscopic, meaning they quickly absorb moisture from the air. As a result, if they are exposed to air, these fluids may contaminate them. Because DOT 3 brake fluid absorbs less water than DOT 4, it accumulates less contamination over time and needs fewer fluid refills. As soon as you fill the fluid, seal the brake fluid reservoir and bottle lid to prevent it from mixing with air.

Viscosity: The viscosity of DOT 4 is greater than that of DOT 3. The viscosity of a fluid is its resistance to flow. Because of its high viscosity, DOT 4 fluid is more tolerant and stable at high operating temperatures.

 

Brake Fluid Specification

Type Dry Boil PointWet Boil PointCompositionMixable
DOT 3401°F/205°C284°F/140°CGlycol EtherYes
DOT 4446°F/230°C311°F/155°CGlycol Ether/Borate EsterYes
DOT 5500°F/260°C356°F/180°CSiliconeNo
DOT 5.1500°F/260°C356°F/180°CGlycol Ether/Borate EsterYes

 

Can I Use DOT 4 Instead Of DOT 3 Brake Fluid?

We can use DOT 4 instead of DOT 3 brake fluid recommended cars and trucks. These two brake fluids’ base fluid is the same, and they are interchangeable. You can safely use the DOT4 with your DOT3 brake system. The only significant difference is the boiling point, and DOT 4 has a higher wet and dry boiling point.

DOT 4 is a better choice for heavy braking like trucks and if you are driving in more hills. Furthermore, the DOT5.1 standard fluid is backward compatible with the DOT3 and DOT 4 standards but cannot use DOT 5 recommended vehicles. Never use DOT 4 recommended systems for DOT 3 fluids. Furthermore, do not use any other oil like engine oil for the brake system.

 

 

Which is Better, DOT 3 or DOT 4?

The DOT 4 is better than DOT 3. These two products are glycol-based brake fluids, but DOT 4 has a higher boiling pot (wet and dry). Therefore DOT 4 consider a high-performance fluid. DOT 3 is considered a standard brake fluid, and DOT 4 is heavy-duty brake fluid.

These two fluids are hygroscopic, which means they can absorb moisture from the air. Therefore, seal the lid soon after you pour fluids into the brake fluid reservoir. Do not allow the brake fluid to mix with air, which will cause reduce service life rapidly. However, DOT 3 absorbs less moisture from the air than DOT 4, making it less contaminated.

 

Brake Fluid Specification

Type Dry Boil PointWet Boil PointCompositionMixable
DOT 3401°F/205°C284°F/140°CGlycol EtherYes
DOT 4446°F/230°C311°F/155°CGlycol Ether/Borate EsterYes
DOT 5500°F/260°C356°F/180°CSiliconeNo
DOT 5.1500°F/260°C356°F/180°CGlycol Ether/Borate EsterYes

 

FAQ.

What is the brake fluid boiling point?

The brake fluid boiling point is the boiling temperature of the brake fluid. It can be divided into dry and wet. The dry boiling point is the boiling point of pure, uncontaminated brake fluid. Typically unopened container fluid boiling temperature. The wet boiling point is the boiling temperature of brake fluid when mixed with atmospheric moisture (around 3.7% water contaminated). It is typically lower than the dry boiling temperature.

 

Can I mix different brands of brake fluid?

You can mix different brands of brake fluids. But it is not recommended to mix DOT 3 and DOT 4 fluids. Since these two products have different boiling points and viscosity, it can reduce the potential performances. DOT 3 is based on polyethylene glycol ethers with additives, and DOT 4 is based on Glycol ether with Borate Ester with additives. Therefore mixing different base fluids is not recommended.

 

Can you mix new brake fluid with old?

It is not recommended to mix old and new fluids. Over time, brake fluids absorb water, and therefore older fluids may be contaminated and not give a potential performance. Before refilling new brake fluids, you must drain them out as much as possible. Contaminated fluids contain water, and when the brake system becomes extremely hot from the operation, the absorbed water can turn into steam. This steam increases the brake system pressure, and you lose control of your brakes.

 

DOT 3 vs DOT 4 boiling point.

If we compare DOT 3 vs DOT 4 boiling point. DOT 4 has the highest dry and wet boiling point and, therefore, has higher performance. DOT 3 has 400°F/205°C wet and 285°F/140°C dry boiling point. The DOT 4 brake fluid boiling point is 445°F/230°C (wet) and 310°F/155°C (dry).

 

Brake fluid what is DOT?

DOT stance for Department of Transport. This is the institute that gives brake fluids ratings based on performance. The rating is based on the fluid’s dry and wet boiling point, and a higher boiling point means higher performance.

 

Is DOT 4 or DOT 5.1 better?

DOT 5.1 has better performance than the 4. It has a higher boiling point and can use DOT 4 recommended braking systems. These two products use the Glycol ether/Borate Ester as a base fluid. However, you should not use DOT 5.1 recommended systems DOT 4. DOT5.1 can use an extremely cold temperature climate.

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