Difference Between DOT 3 And DOT 4 Brake Fluid

One of the most vital components in your braking system is brake fluid. You require it for the car to run smoothly. You should maintain the right amount and keep on changing it regularly since it's the lifeline of the brake system. So how does the brake fluid work?

Difference Between DOT 3 And DOT 4 Brake Fluid

Working Principle of Brake Fluids

Here is what happens in your hydraulic brake system. When you press your brake pedal, it will compress a piston in your brake caliper resulting in a lot of force. That force causes pressure in your brake lines. As a result, your brake rotors squeeze your brake pads. The friction occurs, stopping the motion of the wheels as well as that of the car.

Your brake fluids will obey Pascal's law. Remember, for your car to stop, energy is required. Kinetic energy is that energy that in the motion. When your vehicle stops, the energy will turn into heat. Remember if the mass doubles the energy is supposed to double as well. Meaning if your car has four tons, it will require twice the stopping power compared to a vehicle that is 2 tons. The heat will go into your brake drums/rotor. It will also go into the air as well as the brake fluid. When your brake becomes overheated, it results in brake fade. That's why you require brake fluid.

There are different types of brake fluids. They are in two categories; Glycol-based and the second one is silicone-based. Glycol-based is further divided into different grades. DOT3, DOT4, and DOT5.1. If your car lacks an anti-lock brake system, you require silicone-based fluid.

The most commonly used glycol-based fluids are DOT3 and DOT4. If you are a safari rally driver and you don't want to risk rolling over a cliff, you require DOT 4. If your car involves aggressively applying brakes, you need to use DOT4. Safari rally and police chase cars use DOT4. Unlike DOT3, it can handle the high kinetic energy. If your vehicle doesn't require you to use the brake system aggressively, you can use DOT3. People who drive daily use it. You will find it in most cars and trucks.

DOT 5.1 requires high-performance and heavy-duty applications. Its boiling point is higher compared to both DOT4 and DOT3. It doesn’t absorb water and it’s not compatible with either DOT3 or DOT4. If you have a classic car that you don't use for long, you can use DOT 5.1.

So, are DOT3 and DOT4 compatible? Yeah. DOT3 has a lower boiling point than DOT4 buts it's compatible with it.

Difference Between DOT 3 And DOT 4 Brake Fluid?

Boiling Points

Boiling point is one of the considerable difference between dot 3 and dot 4 brake fluid. Boiling points refers to the temperature under which your fluid will evaporate. It also explains how prone it's likely to absorb the water. DOT3 has a lower boiling point. It's prone to assimilate water. Either hard or rough braking will cause it to boil quickly. This can easily ruin your braking components. It can also create a subpar braking performance. There are two main types of boiling point. The first is dry boiling point. It's determined when you use fluid from a container that is brand new.

Dry Boiling Point
Wet Boiling Point
Composition
DOT 3
205°C/401°F
140°C/284°F
Glycol Ether
DOT 4
230°C/446° F
155°C/311°F
Glycol Ether/Borate Ester
DOT 5
260°C/500°F
180°C/356°F
Silicone
DOT 5.1
260°C/500°F
180°C/356°F
Glycol Ether/Borate Ester

The second is the wet boiling point. It's determined when one uses 3.7% water-contaminated fluid. Is that even possible? Yes, it is. Whenever you want to add fluid, you must remove a reservoir cap. The moisture around your brake system sneaks in, degrading the quality of your oil. You can avoid this by flushing the brake system often so remove any moisture around. The dry boiling point of DOT 3 is 205 degrees C/ 401 degrees F while that of DOT 4 IS 230 degrees C/446 degrees F. Its wet boiling point is 140 degrees C/284 degrees F and that of DOT 4 is 155 degrees C/311 degrees F.

Boiling Capacity

If you were to compare the boiling point of both, then DOT 3 could be the winner. Whether in water or open air, it will still function well. All thanks to its wet and dry boiling points capacity. DOT 4, on the other hand, is excellent in the dry boiling capacity. Unfortunately, it can't work well in water. So if you have a standard car use DOT 3. If you enjoy racing or you drive through rough and hilly roads, DOT 4 would be a better option.

Chemical Structures

The other slight difference between the two is their chemical structure. DOT4 is a mixture of glycol and borate ester. It can handle high-temperature thanks to borate ester. DOT 3 IS based on DEG (diethylene glycol). That makes it cheaper than DOT 4. Note that their chemical structure has no specific requirement. But there is a requirement they need to meet for their wet and dry boiling points. They also require having the right PH value, having water tolerance, stability, and corrosion, among other requirements.

Caution

Whether you are refilling DOT 3 or DOT 4, you have to be careful. If you spill either on your car paint, it will "eat" it. If you mix it with any other fluid that you use in the car, it may react badly. After using them, tightly seal the container. The air moisture degrades their chemical composition if you expose the fluids to it. If you forget to seal the bottle, don't use that brake fluid next time.

Conclusion

You would never want your brakes to fail when driving. That's why you require knowing the right fluid to use and the car that you are driving. If it's a safari rally or a police car you should use DOT 4. If you are not so aggressive with your brake system, use DOT 3. You need to understand their difference in boiling point, their boiling capacity and also their chemical composition. Avoid spilling the fluid on the paint of your car. Never leave the container with the fluid open. If you do, avoid using that fluid.

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