All cars have a brake fluid that can convert the force to brake pressure. It has different numbers like DOT 3, DOT 4, and DOT stands for Department of Transportation.
Can You Use Dot 3 Brake Fluid in a Dot 4 System? You can use DOT 3 brake fluid in a DOT 4 system due to its glycol-containing composition, higher compatibility level, no solvents, and resistance against rust. However, some people avoid it because of variable boiling points, different water absorption, and different replacement intervals.
Many people replace DOT 3 with DOT 4 brake fluid. Both have similarities and compatibility because of their manufacturing composition.
How can you use the DOT 3 brake fluid in the DOT 4 system?
I interchange DOT 3 to DOT 4 brake fluid systems because they have several similarities. Many people use this DOT 3 reliable brake fluid in cars due or the following reasons.
Glycol containing composition
You can use both of these because they have identical compositions. Both comprise glycol as their solvent and offer similar benefits.
However, DOT 3 braking fluid comprises alcohol, glycol, and other additives. The additional additives increase its performance and efficiency.
It has polyalkylene glycol that provides maximum lubrication for the brakes. It has inhibitors of rust which protect the damage to the braking system of flow lines of the fluid.
DOT 4 brake fluid has a complicated composition. But, it comprises glycol, which makes it identical to other options. It has poly glycol ethers and other inhibitors.
These inhibitors can reduce internal oxidation and resist the corrosion of the braking system. Both are similar because of their identification composition.
Higher compatibility level
You can add the low-grade DOT 3 to the high-grade and reliable DOT 4 system.
It cannot change the composition and performance of the DOT 4. Both have no significant differences, which makes them compatible.
However, they have a minor difference which does not allow their mixing. Cars usually use DOT 3, and motorcycles utilize DOT 4.
They have similar functionalities according to their additives and other elements. The cars use both braking fluids for the brake system.
No solvents
You can add this because it is not a solvent, and it has glycol as a solvent which provides higher lubrication.
You can add it to the DOT 4 braking fluid system without fear because it has ether and glycol. It has borate esters, which are reliable and improves its efficiency for the DOT 4 system.
It does not comprise dangerous solvents like acetone and kerosene because they can damage the seals and rubber components. These solvents can cause internal seal damage and affect the brake system.
But, DOT 3 brake fluid does not comprise these dangerous solvents. The DOT 4 braking system does not have these solvents.
Resistance against rust
Adding this is not dangerous because both have rust resistance. DOT 3 lubricant can prevent oxidation and reduces the probability of a thick corrosion layer inside the flow lines.
Furthermore, it is thermally stable and resists heat. Its performance is high and stable at high temperatures. It is chemically stable and protects the seals and other components of the brakes.
It has high lubrication properties and remains stable for providing maximum protection. You can add it to the DOT 4 system and reduce the rusting.
DOT 4 lubricants can cause corrosion and break the rubber-based internal components. Therefore, the DOT 3 lubricant flows inside the system and decreases oxidation.
As a result, the corrosion of metallic flow lines and other metal-based parts reduces.
Difference between DOT 3 and DOT 4 brake fluids
A few people do not add DOT 3 in the DOT 4 brake fluid because they have a few differences. I have explained their non-identical properties below.
| Properties | DOT 3 | DOT 4 |
| Boiling point | 401°F (dry) 284°F (wet) | 446°F (dry) 311°F (wet) |
| Color | Yellow, blue, red, transparent | Crimson red, light yellow |
| Replacement interval | 33000 miles | 47000 miles |
| Hygroscopic | More | Less |
| Resistance to rust | More | Less |
| Cost | $34 | $25 |
Variable boiling points
DOT 4 has a different boiling point than DOT 3. It has a high boiling point which increases its stability at high temperatures.
However, its dry boiling point is 446°F (230°C), and its wet boiling point is 311°F (155°F). The dry boiling point means the temperature limit at which the close brake fluid boils.
The wet boiling point is a specific temperature limit at which the lubricant boils inside the flow passages when it absorbs water. You cannot add the DOT 3 into the DOT 4 system because it has less thermal stability.
It comprises a dry boiling point of 401°F (205°C) and has a wet boiling range of 284°F (140°C). The borates inside the DOT 4 braking fluid stabilize at high temperatures.
Also, it comprises a higher range of ether base that has glycol. The borates esters are part of this lubricant, which makes it resistant to boiling.
Different water absorption
Brake fluids have hygroscopic properties, which means they can absorb water. However, DOT 3 braking fluid and DOT 4 lubricant have different hygroscopic characteristics.
DOT 3 lubricants can absorb around 2% of water annually. The moisture enters the system during the fluid filling procedures.
It leads to broken seals and cracked rubber lines. However, DOT 4 absorbs less moisture according to its composition.
Therefore, some people do not swap these brake fluids.
Different replacement intervals
Some people avoid the addition of DOT 3 lubricant on the DOT 4 car brake fluid system because they have different replacement intervals. The average lifespan of the DOT 3 lubricant is about 33000 miles.
In addition, you can flush and replace it in almost two years. DOT 4 does not require frequent replacements.
It has an average lifespan of about 47000 miles. It has a replacement interval of 2.5 to 3 years which varies according to the braking system condition.
You can find the replacement intervals in the manuals because manufacturers suggest them.
What are the colors of DOT 3 and DOT 4 brake fluids?
DOT 4 and DOT 3 have different colors according to their manufacturing brands and specifications. However, the DOT 3 braking lubricant is available in transparent options.
Also, you can find yellow, red, and blue shades of this lubricant. The DOT 4 lubricant has a light yellow color which makes identification easy.
You can select the crimson red options of this less hygroscopic, reliable, and thermally stable lubricant. You can choose them in any color because their shades do not affect their performance.
Both provide optimized efficiency in any color.
What happens if you put DOT 3 brake fluid in a DOT 4 system?
You can put the DOT 3 braking fluid in the DOT 4 system because it is not dangerous. It does not damage the brake system and fluid flow lines. Furthermore, its safety level is high for the metallic parts of the system.
The metallic parts do not undergo excessive corrosion when you fill them inside the system. However, it has a low dry and wet boiling temperature range, which reduces its stability.
It decreases the stability of the DOT 4 lubricant system, and fluid boils at lower temperatures because this heat level is high.
Low boiling temperature is dangerous and can damage the components of the braking mechanism of vehicles.
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