Brake fluid is the most crucial component in a motorcycle that needs to be taken care of. But, I have seen most of the motorcycle riders are unaware of the fact that their brake fluid also needs to be changed in some time period to have the brake working effectively. In this post, I have discussed brake fluids and you will get all the information regarding them.
So, How often should motorcycle brake fluid be changed? According to motorcycle manufacturers, you should change the motorcycle brake fluids every 2 years regardless of the fluid condition. It may look cleansed or dirty but the effectiveness decreases timely because glycol-based brake fluids are hygroscopic.
Hygroscopic means they absorb moisture aggressively from the environment (air). So, as moisture build-up in the brake fluid, the effectiveness of the brake decreases, and the water build-up in the brake fluid also change the performance characteristic of the brake fluid. Thus, let’s also understand the consequences, if you don’t change the motorcycle brake fluid over time.
What will happen if you don’t change your brake fluid?
If you don’t change your motorcycle brake fluid for a long time then it will lead to poor braking performance or a total brake failure. As motorcycle brake fluid is hygroscopic means it absorbs water from the air. So, over time the accumulation of water level tends to increase, and as you know the brake system with brake fluid heat up as you apply the brakes.
Thus, at high temperatures, the water present in the brake fluid will tend to evaporate and form vapor bubbles. The increasing portion of water vapor in the brake fluid will reduce the brake pressure. It can result in partial or full brake failure which will be a panic situation. Thus make sure to change the brake fluid every two years and check the fluid level every 100 miles.
Also, make sure the brake fluid is sealed completely to avoid contact with air and the formation of these bubbles in the fluids. As the hydraulic system of the brake works on the incompressible fluid to transmit force. For this, the brake fluid must be in a liquid state. That’s the reason the boiling point of these brake fluids is higher than the water.
There was an incident that happened in 2018 due to the lack of awareness for motorcycle brake fluid. Harley-Davidson had to recall 2.5 lakh motorcycles due to the potential brake failure. And, Guess the reason for brake failure, was not changing the brake fluid for a prolonged period.
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According to Harley Davidson, if the DOT 4 brake fluid is not replaced for a prolonged period of time, deposits may create on the elements within the braking system. So, the braking abilities start to reduce.
As we have already discussed that, it’s recommended to changed the brake fluid every 2 years. And, if you delay the change of brake fluid, you may also encounter brake failure one day. So, don’t ignore the brake fluid recycling.
Types of motorcycle brake fluids
There are four DOT (Department of Transport) classifications of motorcycle brake fluids:-
- Dot 3
- Dot 4
- Dot 5 and 5.1
| Brake Fluid Types | Chemical Composition |
| Dot 3 | Glycol Ether |
| Dot 4 | Glycol Ether / Borate Ester |
| Dot 5 | Silicon |
| Dot 5.1 | Glycol Ether / Borate Ester |
Dot 3, Dot 4, and DOT 5.1 are glycol-based brake fluids. While Dot 5 is silicon-based brake fluid.
The basic difference between glycol-based brake fluid and silicon-based is this. Dot 3, Dot 4, and DOT 5.1 (glycol-based) can absorb moisture from the atmospheric air while Dot 5 (silicon-based) can’t absorb water from the atmosphere.
In other words, we can say that glycol-based brake fluids are hydrophilic (attracts to water) while silicon-based brake fluids are hydrophobic (resists to water).
The main characteristic of brake fluid is its boiling point. Because the hydraulic system of the motorcycle depends on the incompressible fluid to transmit force. With incompressible fluid, I am talking about the fluid that is not compressible. While gas is compressible.
Now if our brake fluid got boil then it will get transformed into gas. And, if the brake fluid got transformed into the gas it will lose its main characteristic which is to transmit the force. So, the brake fluid will not be able to transmit the force if it gets transformed into gas. This can result in partial or complete brake failure.
Which brake fluid type should you use in your motorcycle?
As, there are plenty of options to choose from like DOT 3, DOT 4, DOT 5, DOT 5.1. So, how to choose a brake fluid type for your motorcycle.
You should use DOT 4 and DOT 5.1 type motorcycle brake fluid as their boiling point is higher that will provide you effective braking. The higher the boiling point the safer you will be.
The higher the boiling point of the brake fluid the more it will be able to avoid vaporizing in the lines. If the brake fluid state changes, let’s say due to exceeding temperature above the boiling point it changes into a gaseous state then the brake can cause failure and stop working partially or fully.
Now, let’s understand the boiling point for the motorcycle brake fluid. There are two types of boiling points specified. One is the wet boiling point another is the dry boiling point.
The major difference between both is the presence of moisture and the absence of moisture. The wet boiling point is calculated after some moisture is added to the brake fluid. While the dry boiling point of the brake fluid refers to its original state where there is no moisture absorbed.
Here in the below table, I have included both the boiling point for every brake fluid type:-
| Brake Fluid Types (DOT) | Dry Boiling Point | Wet Boiling Point |
| DOT 3 | 205 °C (401 °F) | 140 °C (284 °F) |
| DOT 4 | 230 °C (446 °F) | 155 °C (311 °F) |
| DOT 5 | 260 °C (401 °F) | 180 °C (356 °F) |
| DOT 5.1 | 260 °C (401 °F) | 180 °C (356 °F) |
Now, at this point, you may have noticed that the boiling point of DOT 5 and DOT 5.1 are the same. You may be thinking, So, what’s the difference between DOT 5 and DOT 5.1?
The difference between these two DOT types is of chemical composition, DOT 5 is made with silicone whereas DOT 5.1 is made up of Glycol Ether. Dot 5 is hydrophobic while DOT 5 is hydrophilic.
So, you should use DOT 4 and DOT 5.1 as these have higher boiling point than reduce the chance of brake failure in most of the case.
Can you mix different brake fluids?
Even though the brake fluids meeting the DOT specifications are compatible but mixing of brake fluid is not recommended. You should never mix different composition brake fluids in the system. Like Dot, 5 brake fluid should not be mixed with Dot 3 or Dot 4 as their chemical composition are different.
The mixing of two different chemical composition brake fluid types will result in a decrease in performance and cause interference in the pressure transfer. So, you should never mix two different types of chemical composition brake fluid.
Although, the mixing of the same chemical composition brake fluid will be acceptable. Like mixing of DOT 4 and DOT 5.1 as both are made of glycol.
Conclusion
Thus, after reading this you must have realized the importance of taking care of brake fluid. Brake fluids are important as they provide the required pressure to the brakes as you apply.
Just make sure to change the brake fluid every 2 years and check the level of it every 100 miles. This is the best way to ensure the effectiveness of the brake fluids. There is a lot to talk about brake fluid which I am planning to cover in upcoming posts.
FAQs
Does motorcycle brake fluid go bad?
Yes, motorcycle brake fluid goes bad with time. With time the brake fluid absorbs moisture which can decrease the braking performance. And if absorbs too much of it then the braking may be partially or completely fail. Then it can result in serious trouble for you. Thus, make sure to flush your motorcycle brake fluid every two years.
