There are 3 types of brake fluid available in the USA and choosing the right one for your particular situation is an important part of building your project. We will discuss the advantages and disadvantages of all 3. Then you will be able to make the decision on which one is right for you.

Dot 3
By far the most widely used by both import and domestic vehicles at the OE level. Dot 3 is highly hygroscopic meaning that it attracts moisture. If you read on the label of the Dot 3 or Dot 4 container it will say "keep container tightly closed to prevent absorption of moisture". The minimum "wet boiling point" (meaning with a 5% water content) is 284 degrees F.

The advantages of Dot 3 are as follows;
1. readily available at any parts outlet
2. easy to work with
3. reasonably priced

Disadvantages are;
1. attracts moisture
2. removes or damages paint

If you have ever bled a vehicle that is 5-6 years old and it was originally equipped with Dot 3 or Dot 4, you will notice that the fluid that comes out of the system during the bleeding process looks like muddy/rusty water. That is because that is precisely what it is. The highly hygroscopic nature of Dot 3 and Dot 4 will pull moisture from the air in the form of humidity right through your porous rubber brake hoses and contaminate and corrode the inside of the brake system and lower the boiling point of the brake fluid in the process. If you own an American made vehicle built since 1972, your owner's manual will recommend a brake system flush every 1-3 years. I don't know anyone who does this, but if they did the hydraulic parts would outlast the vehicle

Dot 4
Wet boiling point is 311 degrees

Dot 5 (silicone brake fluid)
Advantages
1. non hygroscopic
2. will not harm paint

Disadvantages
1. very expensive
2. somewhat susceptible to aeration if not handled carefully
Note: Dot 5 is not recommended for systems with ABS

Dot 4 is the same thing as Dot 3 with a slightly higher wet boiling point
I hope this short article gives you some insight on the brake fluid best suitd for your particular application.

As always, you can find me on the BBS most every evening and I will be delighted to answer any questions you may have.p> "Fat Pat" Anderson

Monday, August 14, 2006