How to know what brake fluid you have ?

[Racer57]

Is there anyway to tell which type of brake fluid you have ?

[Chryco Psycho]

Dot 5 has a purple color to it , dot 3 or 4 will eat paint , put it on a sample away from the car & see what it does to paint .

[JH27N0B]

I don't know why, but I've found when bleeding a system that has DOT 5, what I drain from the system doesn't have the purple hue to it anymore.  In fact, I have a jar of DOT 5 brake fluid out in my garage leftover from when I was filling and bleeding one of my car's brake systems.  A restoration with entirely new parts and NOS parts used for the brakes, and the drained fluid isn't purple.  It was purple when I poured it from the containers of brand new DOT 5 brake fluid!
The OP poses an interesting question which I'm not sure what the best answer is.  Certainly DOT 3/4 and 5.1 has a unique smell to it which DOT 5 smells different. Maybe feels different if you rub a bit on your fingers also?
I'm reminded of a funny story years ago when I rented a room at my house to a friend who had a new Gold Wing he parked in my garage.  I was working on my T/A's brakes bleeding them.  He came out and said "I don't like you working with brake fluid near my bike!".  I said, "it's DOT 5, it's silicon brake fluid and won't damage paint.". He said "I still don't like you working with brake fluid by my bike!". So I picked up a container of the DOT 5 brake fluid, poured a splash on my fender, grabbed a cloth, started rubbing it, and said "look, it's silicon, I can wax my paint with it!!".  He again said he didn't like me working with brake fluid by his bike.  I said fine, don't park it in my garage then...".
Some people just can't admit they are wrong about anything I guess. 

[Racer57]

I don't know why, but I've found when bleeding a system that has DOT 5, what I drain from the system doesn't have the purple hue to it anymore.  In fact, I have a jar of DOT 5 brake fluid out in my garage leftover from when I was filling and bleeding one of my car's brake systems.  A restoration with entirely new parts and NOS parts used for the brakes, and the drained fluid isn't purple.  It was purple when I poured it from the containers of brand new DOT 5 brake fluid!
The OP poses an interesting question which I'm not sure what the best answer is.  Certainly DOT 3/4 and 5.1 has a unique smell to it which DOT 5 smells different. Maybe feels different if you rub a bit on your fingers also?
I'm reminded of a funny story years ago when I rented a room at my house to a friend who had a new Gold Wing he parked in my garage.  I was working on my T/A's brakes bleeding them.  He came out and said "I don't like you working with brake fluid near my bike!".  I said, "it's DOT 5, it's silicon brake fluid and won't damage paint.". He said "I still don't like you working with brake fluid by my bike!". So I picked up a container of the DOT 5 brake fluid, poured a splash on my fender, grabbed a cloth, started rubbing it, and said "look, it's silicon, I can wax my paint with it!!".  He again said he didn't like me working with brake fluid by his bike.  I said fine, don't park it in my garage then...".
Some people just can't admit they are wrong about anything I guess. 

I was expecting you to say that you poured it on his bike.  I would've.   

[RUNCHARGER]

Ha, ha: In my younger years I would dip my models in brake fluid when I wanted to repaint them.

[GoodysGotaCuda]

Dot 5 has a purple color to it , dot 3 or 4 will eat paint , put it on a sample away from the car & see what it does to paint .

My DOT 5 quit looking purple after a few days of being out of bottle. 

Most every car will have DOT 3, some savvy owners with upgraded brakes will have DOT 4, if the brake system [and or paint] is 100% new, it may have DOT 5. There may be some test strips available for some of it, the paint test will help, so would applying water to a sample.

[Cudakiller70]

I found this elsewhere seems like a reasonable test 


You need to find out which you have already in the system. Here's how:-
1. Get a dropper (an eye or ear-dropper) and withdraw some fluid from the master cylinder.
2. Put it into a glass jar and then add some clean water to the fluid.
3. Now put the lid on the jar and shake it well.
4. Let it stand for a few minutes.
5. If the water and the fluid have mixed thoroughly and can not be separately identified, then you have regular auto brake fluid.
6. However, if the water and the fluid have not mixed, or have formed blobs or layers, then the fluid is Silicone.

That's all there is to it. Lots of people think that you can recognise which is which by looking at the colour of the fluid, or by its odor. Don't risk it. Use the test outlined above. It's already been said that DOT 5 is not always purple, or that it can change color after time to a yellow that looks like DOT 3.

[Chryco Psycho]

Makes sense , thanks !

[RUNCHARGER]

Yes: That looks like easy conclusive test.