The brake system is one of these things which are very important to take care of because you really want it to function properly in an emergency situation.
The brake fluid is one of these things that you need to replace every one or two years otherwise, it may cause rust inside the brake system and damage other parts.
There are two general types of brake fluids are produced: silicone or glycol basis. Dot3 and Dot4 are popular glycol-based brake fluid options available for many vehicles. While Dot3 is popular with normal drivers, Dot4 is more common in newer car models.
But what is the difference between them and can you mix them with each other?
Dot 3 vs. Dot 4 Brake Fluid Differences
Both Dot 3 and Dot 4 brake fluids are glycol-based products used in your braking system. They are hygroscopic and absorb water from the atmosphere, which means that care must be taken when storing and regularly replacing potentially contaminated fluids. But what is actually the difference between them?
The main differences between the Dot 3 and Dot 4 brake fluid are the boiling point. The Dot 4 brake fluid does have both a higher wet and dry boiling point and is better suited for higher performance, which you can see in the table below:
|Type||Wet Boiling Point||Dry Boiling Point||Composition|
|DOT 3||400°F/205°C||285°F/140°C||Glycol Ether|
|DOT 4||445°F/230°C||310°F/155°C||Glycol Ether/Borate Ester|
|DOT 5.1||500°F/260°C||355°F/180°C||Glycol Ether/Borate Ester|
Can you mix Dot 3 and Dot 4 Brake Fluid?
Yes, both Dot 3 and Dot 4 brake fluids are glycol-based brake fluids, which means that they are compatible with each other, and there is no problem at all mixing them.
If your car has Dot 4 from the factory, you should never refill it with Dot 3, though; but the other way is fine.
If you have Dot 3 in your car from the factory and you know that you are often driving with a trailer or in steep hills, I strongly recommend refilling it with Dot 4 instead.
Can you mix Dot 5 with dot 3 and dot 4?
Dot5 is a silicone-based brake fluid. It does not absorb water from the air and is not compatible with ABS systems. It maintains its integrity and works well. It also has a higher boiling point than the brake fluids Dot3 and Dot4, making it more compatible with excessively aggressive driving.
However, it is not compatible with Dot3 or Dot4 liquids and should never be mixed with them. You must also follow your manufacturer’s recommendations to know whether your braking system is compatible with Dot5 brake fluid.
What does the boiling point mean?
As we told before, Dot 3 and Dot 4 brake fluids are hygroscopic, which means that they absorb water over time. This is the reason why you should replace it every year or 2nd year.
When you drive your car hard at hills or with a trailer and braking a lot, the brake fluid will heat up fast. If it is heating up too much and starts to boil – you will lose the ability to brake your car, which is the least you want to happen at a hill with a trailer. Therefore it is important to have such a high boiling point as possible.
The wet boiling point is measured when the brake fluid contains water, and the dry boiling point is without water.
Dot3 vs. Dot4: Which one is the better brake fluid?
Dot3 is the more popular of the two brake fluids, but Dot4 is quickly gaining popularity because it is compatible with the standard traction control and anti-lock braking system.
Dot 4 has higher boiling points, making it better for all types of applications; even though it is often a little bit more expensive, it is worth getting it instead.
Hi, I’m Magnus, the owner and the writer of Mechanic Base. I have been working with cars for 10 years, specialized in diagnostics and troubleshooting. I created this blog because I was tired of finding false information on the web while looking for repair information. I hope you enjoy my content!