My son was bleeding brakes (still working on it, getting a replacement rebuilt caliper today) and left the fluid out in a large open glass jar for a couple of days. Is it still good or ruined? (it's new, we've bled the brakes 5 times or so, so I'm trying to re-use new fluid). I've already gone through 4 liters or so.

I used to be lax about brake fluid, using old but sealed containers and bleeding just enough to get any air out of the caliper(s). The braking was not impaired short-term, but I found I had to do brake jobs every few years.

My understanding from reading on the subject on this forum is that using pristine brake fluid will keep your brake system in working order for a much longer period of time. I adopted this approach about a year ago, and am still awaiting the long-term results, so far with success.

Last time I replaced both back calipers, I bled 1 litre through the lines, but I could have stopped at half that amount. 1 litre should be enough to bleed the whole system.
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'92 245 5-speed, '92 944 GL auto

The industry rule is that any fluid bled out of a system is not to be returned to the system, but discarded. I have always done that. A wide open container will absorb substantial moisture in a few days. I would discard it as well.
Four litres is a huge amount of fluid. On a complete brake job, four calipers and a master I will use about 1/2 to 3/4 of a litre to get a good pedal. Something is wrong with a component or your method.

The reason for not reusing fluid bled from the system could be the cause of your soft pedal. When the fluid spurts out, it becomes aerated. Some of the bubbles are visible, others are so small as to be microscopic. The larger ones will rise to the top of the container and escape, but the tiny ones will remain for a long time. Air is air, no matter what size the bubbles are, and it is compressible.

If you have been reusing the fluid, I would start over again and bleed everything until you are sure you have all new fluid in the system.

There is a racing brake fluid (I forget the brand) that comes in two different colors that are otherwise identical so you can be sure you have gotten all the old stuff out.

Maker of the dyed fluid is the maker of your rear 200 calipers.

I believe a component is bad - I think one caliper might have mismatched halves - the dimples are not obvious like they are on the other rebuilt caliper, everything has been "done by the book".

I wouldn't worry about that, if it was clean to start with...

But that's me. I know guys with 15 yr old brake fluid who don't worry either, but that might be overkill.

It all depends what you expect to get out of the car.

Greg

Well considering that he left the brake fluid open in a large jar for a few days, I think he should strain out the dead bugs first.
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1980 245 Canadian B21A with SU carb and M46 trans in Brampton, Ont.

I'd be more worried about the live bugs. Anything that crawls out of a jar of brake fluid may be destined to take over the world.
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A smart bomb. The bomb teaches Shakespearean sonnets, ancient cuneiform, relativity, and the Tibetan language. It may know other things. It has no tolerance for rudeness, so ask nicely.