Brake fluid turned green; why?

[bulwnkl]

What makes brake fluid turn green, when it starts out light tan to gold?

Flushed the factory fluid on one of my vehicles after 2 1/2 years. It was distinctly darker than new, but just brown. Fast-forward 2 1/2 more years to the next flush. The fluid in the master cylinder, all the calipers, and throughout the lines was green. Probably darkest (not by much) in the master cylinder reservoir, but at least the one caliper was also that dark.

Both 2 1/2 years ago and yesterday the old fluid was also distinctly more opaque (cloudy).

Why did this fluid turn green? Is that just the color they intend for it to turn as it ages and breaks down? When new, the fluid is very light tan or gold, as with most common brake fluids.

NOTE: In a different vehicle, the same fluid was flushed at about the same time. Flushing that vehicle yesterday, there was no trace of green. The old fluid was a bit darker than new, but that's it.

 

[gathermewool]

Copper or Cu/Ni anywhere in the lines?

 

[slacktide_bitog]

GM cars do this a lot. Green brake fluid is very common with GM.

 

[maxdustington]

My BF was green and gross as well. I think it's from the ABS pump, I can't think of any other sources of copper in the braking system. I'm not a mechanic or automotive engineer though.

 

[Kestas]

Copper comes from the brake lines, which are made with Bundy tubing.

 

[bulwnkl]

Right, there's (commonly or usually) copper in steel brake lines. Is the thought that the fluid is green because it's attacking brass? If so, I'm struggling with the notion of a _very_ common brand of brake fluid being so active against brass or copper-containing parts that its inhibitor system can't last 2 1/2 years in nearly the driest climate on the continent. However, it _could_ happen, I suppose. For those who believe that to be the case, what brake fluid(s) in your experience are the worst in terms of anti-corrosion durability.

Or do you think there's some other issue here?

 

[Kestas]

Working from memory, I believe there are test strips used to check the condition of brake fluid. These test strips check for copper content.