How to determine what type of brake fluid?

[Ken K.]

Is there a way to determine what type of brake fluid you have in the car? (Silicone or DOT 3 type.) I have not had the car long and I want to bleed the brake system. I was thinking about spray painting a scrap piece of metal and then put a few drops of the brake fluid on that paint surface and see what happens. Would this work?
Thanks Ken

[Duke W.]

Re: How to determine what type of brake fluid?

A better way is to draw off a sample and mix it with some water - say about equal parts brake fluid and water, then let the sample stand for awhile. Conventional glycol ether based fluid (DOT 3, 4, 5.1) is miscible with water and will not separate.

Silicone (DOT 5) is not miscible with water and will separate.

Duke

[Phil P.]

Re: How to determine what type of brake fluid?

i've seen silicone brake fluid disolve paint on my friends street rods---i would'nt trust that test

[Frank C.]

Re: How to determine what type of brake fluid?

Ken...the DOT 5 silicone brake fluid I use is GE and is purple in color. It is very easy to see, however I don't know if all brands have color code. It is highly believed and advertised not to harm paint, but I'm going to test it.

[Terry M.]

Re: How to determine what type of brake fluid?

The purple additive used in DOT 5 will deteriorate over time and fluid after five years of so of use looks golden brown. The separation test cited above is simple and effective.

I would suggest your street rod friend got something besides DOT5 brake fluid. Other than making a quality repaint difficult, silicone brake fluid will not harm and already cured paint job.