Brake fluid, a type of hydraulic fluid, is used in vehicles to move various parts of the braking system. It is mainly applied in the hydraulic clutch and hydraulic brake of a vehicle to add pressure and increase the brake force. This type of fluid works well under high temperatures and pressure. Since liquids are non-compressible, brake fluid is no different. When you press down the brake pedal, brake fluid delivers force into the front and rear brakes of the vehicle, which causes it to stop.
In the hydraulic brake system, when the driver of the vehicle engages the brake pedal, it, in turn, compresses a piston, found inside the brake caliper. This force causes the pressure inside the brake lines to increase, which activates the brake fluid. When this happens, the pressure inside the brake fluid makes the brake rotors to press down on brake pads, which then makes contact with the wheels of the vehicle, causing them to slow down and stop.
There are different types of brake fluids but two of these fluids are commonly used by drivers; these are glycol-based fluids and silicon-based fluids. While silicon-based fluids are applied only in vehicles without the anti-lock based system, glycol-based fluids are used in vehicles with anti-lock based systems. The DOT (Department Of Transport) categorizes the different types of fluids according to their specifications. Some of the most critical specifications of brake fluids are their boiling points and chemical composition. The brake fluids as classified according to their boiling points are DOT3, DOT4, DOT5, and DOT5.1.
The glycol-based fluids need to meet specified standards as stated by the government, which include chemical stability, water intolerance, PH values, and oxidation resistance. The most commonly used type of fluid by vehicles is DOT3 since it is not over aggressive on their braking system. The DOT4 fluid is mainly used in racing and police cars because it has a higher boiling point.
Here, we will discuss some of the differences between Dot3 and Dot4.
1. Boiling Point
The DOT (Department Of Transport) classifies the brake fluids according to their specifications, where a boiling point is one of the most important. Their numbers are arranged from the lowest to the highest with Dot3 having the lowest. The boiling point is the temperature with which the fluid evaporates when applied.
There are two types of boiling points; dry boiling point and wet boiling point. The dry boiling point is for fresh fluids, while the wet boiling point is for fluids that have absorbed moisture.
Dot3 Boiling Point
In glycol-based fluids (view on Amazon), Dot3 lowest boiling point of 205 degrees Celsius/401 degrees Fahrenheit at dry boiling point, and 140 degrees Celsius/284 degrees Fahrenheit at wet boiling point. Due to its low boiling point, Dot3 absorbs water, which increases the hand braking chances of boiling.
Dot4 Boiling Point
The Dot4 fluid has a higher boiling point than Dot3. At dry boiling point, it has 230 degrees Celsius/446 degrees Fahrenheit and 155 degrees Celsius/ 311 degrees Fahrenheit at wet boiling point. Its higher boiling point reduces the chances of boiling.
However, both fluids are hygroscopic, which means they absorb water. According to their boiling points, the Dot4 is mostly preferred since it can handle more heat.
2. The Chemical Composition
Dot3 and Dot4 braking fluids also differ in chemical structure. In spite of these differences, these fluids meet the minimum requirements to be used in braking system.
Dot3 Chemical Composition
The Dot3 fluid is composed of diethylene glycol (DEG). While it is not a mandatory for it to be used in fluids, most manufactures prefer to use it since it is the most economical way for them to meet the minimum requirements set by regulators. It is concluded to be standard.
Dot4 Chemical Composition
The Dot4 fluid comprises of glycol and borate ester. The component, borate ester, enables the Dot4 fluid to handle high temperatures. It is evident as it has higher boiling points, in both dry and wet form, and its chemical composition has enabled it to absorb less water and tolerate high temperatures.
Both Dot3 and Dot4 composition tend to meet the stated standard requirements. However, the borate ester in Dot4 gives it an advantage over Dot3 because of its ability to work well even in high temperatures and its high water tolerance.
3. The Boiling Capacity
In regards to the boiling points, both Dot3 and Dot4 have a different boiling capacity. Their boiling point in both dry and wet determines the boiling capacity when applied.
Dot3 Boiling Capacity
The Dot3 fluid works well both in the open and in water since it has both dry and wet boiling points. This makes it suitable to be used in standard vehicles, as it is not aggressive on the braking system. It is, therefore, more convenient.
Dot4 Boiling Capacity
Despite Dot4 fluid having a high dry boiling point, it does not work efficiently in water, which makes the fluid less suitable for standard cars, as it can be over-aggressive on the braking system of vehicles. The Dot4 fluid is commonly found and works best in police vehicles and racing cars.
For drivers of standard vehicles, it is advised to use Dot3, whereas fast racing cars use Dot4 since it has a higher boiling point. However, Dot4 can be used in the anti-lock based system, which has made it more widespread.
4. Water Tolerance
Both fluids, Dot3 and Dot4, are hygroscopic, which means they absorb moisture through microscopic pores immediately they are applied on the hydraulic system or when exposed to air. When water enters the hydraulic system, it is spreads all through the brake fluid because it is heavier than the fluid. If the boiling point of the fluid is high, the water will boil faster than the fluid.
Dot3 Water Tolerance
Since it has a lower boiling point, Dot3 tends to absorb more water. Determine this by testing using the dry and wet boiling points. The Dot3 fluid works well in its dry boiling point. Since the fluid is from an air tight container it has not absorbed any moisture until it is opened. When used in wet boiling point, the quality of the fluid will reduce since the fluid has absorbed 3.7% of the water from opening the reservoir cap to add the fluid.
Dot4 Water Tolerance
The Dot4 brake fluid has a higher boiling point than Dot3, which makes it tolerant to water. Its ability to handle high temperatures makes it absorb less moisture. Therefore, they perform well in both dry and wet boiling points. Additionally, its chemical composition makes it easier for it to improve its water tolerance level.
The Dot3 will work better in dry boiling points, while Dot4 works well in both. It is noted that each time you open the reservoir cap to put in fluid, the fluid absorbs moisture thus reducing in quality. It is advisable to flush the brake system to remove the moisture regularly.
Can Dot3 and Dot4 be compatible? The compatibility of brake fluids depends on their boiling points and water absorbance capacity. Brake fluids with a higher boiling point can perform well in the lower boiling points system, while brake fluids with a lower boiling point cannot work well in a high boiling point system.
The Dot3 fluid cannot be used in the system adapted for Dot4 fluid. This is because it has a lower boiling point and has high water absorbance, which does not fit in the Dot4 system. Since it is mainly found in regular cars which do not need aggressive force on their brake system, using it in Dot4 system can cause brake failure.
It is possible to use Dot4 fluid in place of Dot3. When using Dot4 fluid in the Dot3 system, completely get rid of the Dot3 fluid in the system to make it possible for the Dot3 system to take in the benefits of Dot4 fluid fully. These benefits are the high boiling point in both wet and dry, which makes it absorb less moisture.
In essence, Dot4 is compatible with Dot3, while Dot 3 is not compatible with Dot4. Also, Dot3 and Dot4 cannot be mixed with other fluids as they are incompatible. When mixed accidently or deliberately, your car braking system will cause break down.
By and large, Dot3 and Dot4 fluids do not vary so much in functionality. The main difference between the two is their boiling point and chemical composition. These two specifications are the primary roots of their differences since it narrows down to their performance. The chemical component in Dot4, borate ester, is the substance which gives it a higher boiling point than Dot3, in both dry and wet boiling point.
Dot4 seems to have a slight advantage over Dot3 because of its ability to endure high temperatures and high water tolerance. However, most regular drivers who drive standard vehicles prefer Dot3, because it makes their car perform well.
Brake fluids are essential to all vehicles, and each has its specified fluid to use. Drivers and owners of vehicles should be keen on the type of fluid they use for their vehicles as specified.
You Need to Know This About Brake Fluid
Routine maintenance is a good way to prolong the life of the braking system. The brake fluid can be inspected when the car goes in for an oil change. When a vehicle is not serviced regularly, things build up. The bore inside the master cylinder can become corroded, which results leaks in the seals.
If you want to avoid brake fluid problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.
A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.
Other Important Points to Note
- When using both brake fluids, you should ensure not to spill the fluid on the body of your vehicle since they can remove the paint of the vehicle altogether.
- Also, do not mix the fluids with other fluids. Doing this may result in a dangerous or adverse reaction, especially Dot5, which does not absorb any moisture due to its high boiling point.
- For storage, always ensure that you keep them in tightly sealed containers, which is because, when opened, it may absorb moisture which reduces the quality of the chemical composition of the fluid. With this in mind, also avoid using fluid from an open container as it will not perform as expected.
- When changing brake fluid of the vehicle, always read and follow the instructions of the manufacturer, especially when you are not sure of what to do.
- It is also important to change brake fluid from time to time since they can wear out. Without this regular changing, the increased absorbed moisture might damage the metal components of the vehicle, and the brakes may become spongy, which is dangerous. For standard vehicles, it is advised to change the fluid regularly every year, while for racing vehicles; you can change the fluid every year.
- Do not mix Dot3 and Dot4 as it may result in brake damage issues. Always consult the manufacturer and only use the specified fluid for your vehicle.
- Be keen on brake maintenance as it is a significant part of the car, whose failure may cause severe damage to the car.