Brake Fluid - How do I know which type?

[terryp]

I've had the car about 9 months and this is the first time I have had to do anything to the brakes.
I need to add some fluid/bleed, how do I tell which type of fluid has been used in the past?
Mineral , semi , silicone , Dot 3, Dot 4 or Dot 5
The clutch master cylinder and slave cylinder were changed and that has Dot 5 as there is a label on that pipe. Also there is some Dot 5 fluid with the car
Any ideas anyone?

Thanks a lot

Terry

[Jason1]

Hi

Interesting question; I believe the DOT rating refers to the boiling point of the fluid.

Boiling points from Wikipedia; so could be rubbish

Boiling point ranges
Dry boiling point Wet boiling point
DOT 3 205?C (401?F) 140?C (284?F)
DOT 4 230?C (446?F) 155?C (311?F)
DOT 5 260?C (500?F) 180?C (356?F)
DOT 5.1 270?C (518?F) 191?C (375?F)

But to measure the boiling point of any fluid you remove from the system you would have to be certain that the fluid was pure; as any water in the fluid would reduce the boiling point.

The short answer is I do not believe you can, the best thing to do would be to bleed the system and refill.

It is however still an interesting question

Jason

[terryp]

Jason
Ive been searching on the net as well and apparently you can!!!!
You remove some brake fluid using a dropper , mix it with water, if it mixes its standard, if not and blobs (and behaves like silicone) its silicone!
Mine looks like silicone, has anyone else ever done this?
Does it work?

Terry

[RichC]

my silicone fluid is purple .I imagine that may be standard?. ordinary is greenish.

[terryp]

ITS PURPLE !
So its silicone then,
Thanks to all

Terry

[Jason1]

Hi

Sorry I have never used silicone fluid, I decided to use good old Castrol (think it was yellow wee colour?) when I rebuilt my brakes. If you search the forum you will see there are varying opinions on the use of silicone; I decided it was not worth the risk.

Jason

[bcmc33]

There was a good thread on this subject a short time ago, and I saved the following which I thought was well worth keeping for future reference:

http://www.stoptech.com/tech_info/wp_br ... d_1a.shtml