How to tell if you have dot 3,4,5 or silicone brake fluid

[JL66REDCPE]

I need to change the brake fluid in the car. How can I tell if the fluid in there is dot 3,4,5 (non silicone) or silicone.

I was wondering if I could put a small amount in a jar and add water and see if it separates -- however I am sure there is a better and easier way.

 

[stepinwolf]

Three or four I " don'no ", but five is easy

Dot-5 will not lift paint, so take a part that has been recently painted, and choose an inconspicuous place to put a drop of brake fluid on, wait a few seconds, and rub. If the paint stays it's Dot-5, if not, then your choices are down to two.

You can't mix Dot-5 with the other two, but I do not know if there would be a problem mixing 3 and 4 together. Maby some other member can address your last choice.

 

[vetzs]

Is it ok to answer on behalf of John Z? One of the many things I have learned from him and others is:

Put equal amounts (an ounce or two) of whatever's in your master cylinder and water in a glass jar, shake it up, and set it on the bench. If two distinctly different layers form, that's the water on top and the DOT5 silicone fluid (heavier than water) on the bottom. If the result is a homogeneous mixture with no layering, it's DOT3/4 glycol-based regular fluid. John Z

 

[JohnZ]

You can't mix Dot-5 with the other two, but I do not know if there would be a problem mixing 3 and 4 together. Maby some other member can address your last choice.

DOT3 and DOT4 are totally compatible; both are glycol-based, and the only difference is that DOT4 has a slightly higher boiling point and an improved corrosion inhibitor package.

 

[JL66REDCPE]

Thanks all for the replies

 

[JL66REDCPE]

Well , I bled the brakes this weekend and mixed water and the some of the drained fluid in a clear container. I became a solution and pretty much stayed that way meaning I have Dot 3 or 4. I was really surprised at the sediment in the mixture. It looked like rust particles and it looked like it only came out of the passenger side front caliper which was where the air seemed to be. Any comments on just the sediment appearing from one brake.

 

[Viet Nam Vett]

Well , I bled the brakes this weekend and mixed water and the some of the drained fluid in a clear container. I became a solution and pretty much stayed that way meaning I have Dot 3 or 4. I was really surprised at the sediment in the mixture. It looked like rust particles and it looked like it only came out of the passenger side front caliper which was where the air seemed to be. Any comments on just the sediment appearing from one brake.

How old is your fluid?? Is it as old as you and that is why your changing it?

Or..did you have a stopage problem or a soft Non Viagra Pedal..?? :L

 

[JL66REDCPE]

Mark - It had a low pedal. If you just pushed on the pedal to use the brakes it was too low however if you pumped it once or twice it was fine. It has always had a hard pedal -- never a soft one. The brake fluid is definitely old. Just another thing to add to the already long list.