OK, so I know that it is hygroscopic and will start absorbing moisture as soon as it is exposed to air. But how long is an opened can (of ATE Blue) good for on the shelf? How long is too long?

I ask WRT my Trackmeister as that obviously gets frequent bleeds. But as I just had to replace one of the hard lines today, I still have a 1/2 can left. I don't want to throw that away if it'll still be good for a month or two. Talk to me ...especially those "in the know." (ahem, Steve? Pete? )
TIA!
...oooh, just a thought, should I have put this out on the Racing forum?

Edward

 

Edward,

A few years ago, I did a test trial of a nifty Leica instrument made specifically to determine water content in brake fluid and thus, changes in boiling point.

Quite revealing,....

Unless one lives in a desert climate where RH's range under 20%, I do not use brake fluid containers that have been open more than 60 days. Less, in more humid and/or wetter climates. Mind you, this is in the context of cars used for track use.

Brake fluid is SOOOO cheap that there is no economy in stretching its use and I've witnessed the folly of that particular practice. The body shop bill was FAR higher than a few litres of brake fluid.

JMHO, of course.

 

+1

 

I boiled the fluid on my 12K mile street TT's PCCBs recently during a spirited run up and down Mt. Palomar. I was with a bunch of 993s none of whom boiled theirs. To be fair, I was enjoying boost checks and hard braking while they were enjoying momentum. We took a 15 minute break and the slightly soft pedal went away then and for the next 2K miles until I took it in for a scheduled service at the dealer.

Despite the good advice on SRF in

https://rennlist.com/forums/showthre...il+brake+fluid

I stuck to the OEM fluid when I had it flushed. As recommended by the dealer service adviser for my typical street driving. He may not have had SRF on hand. If it happens again I am switching to SRF.

 

Interesting. I have a 1/2 full standard metal can with plastic cap of ATE blue that is over 5 years old. I test it every year or so and so far the BP has dropped about 9 deg. I test with a true boil point tester that heats the fluid until it boils and notes the temp at that point. No calulations or tables, true boil point. I run it on new fluid now and then and it hits the dry points noted on the can within a deg or 3 so it think it is reasonably accurate. Dry point to wet point per DOT is 3% water take up.
I also had a 1/2 full plastic container of FLAPS brake fluid that went from rated point to 250 deg in a year after being opened only once. both are stored in a shop subject to high 90%+ humidity in summer an in fully unconditioned space for the first 3 years. I think metal cans not left open store longer than plastic.
I have also tested the fluid in cars during use and noted that the worst moisture take up is in the reservoir. Bleeding fluid from the reservoir to the calipers might just be moving the worst fluid in your system to the area where moisture is most unwanted, the heated parts. Based on this I now always remove the fluid and top with fresh before any bleed or flush. Fluid is cheap but good methods are free.

 

Part of my job is moisture testing and water vapor transmission...

The container for ATE fluid (can and well constructed cap) is not going to allow any significant moisture change when it's closed. What will matter more is how long you have it open (do you pour fluid back from the bleeder into the can? - don't). The ATE can is likely as good or better at protecting the fluid than the reservoir in your car and the rest of your brake system. (The reservoir is plastic and plastic is permeable to moisture.)

Kurt: There is unlikely to be much difference in the moisture level at the caliper or the reservoir due to diffusion - the water level will equilibrate.

That said, and while we all should want to protect the environment, it doesn't make sense to try and save $6. I use a fresh can every time.

 

That is exactly what I expected to find and was suprised when my (limited non benchmarked) data did not suport it. All a guess but perhaps the MC acts as a block of sorts or the lines being long and small dia or a limited difusion pressure might slow the migration of H2O as well. My testing might be off but in the tests of 6 systems that were filled with non disturbed at least 5 months fluid there were measurable deltas on all but one. That one was a 6 month old SRF system that had been well flushed during a switch over from standard DOT4 and was an A/C garage queen. Testing was done during east coast summer in an area where humidity is measured with a knife and buckets. Hightest deltas were in 2 track only cars that were unused other than on track weekends.

I am not making recomendations based on my testing only reporting what I have seen myself. I flush based on testing rather than any rule of thumb.

 

Thanks, all. And Steve, your empirical knowledge is, as always, indispensible! You too, Tom, it's awesome to have experts in the field!

I never prescribe to false economy, and as such ALWAYS bleed with a fresh can of ATE before a track event. Cheap insurance as they say, and brakes are the LAST thing I want to be concerned about on the track. But my question was really intended to (hopefully) save that 1/2 or more can of newly-opened SuperBlue for an event in October. So in its closed can on a cool/dark shelf in my SoCal garage , I suppose it'll still be good in 2 months. Thanks all!

Edward

 

Since you bleed the brakes before every event, as you should, you simply need to do more track events to solve this dilemma!

 

LOL! Thanks, Bob. I'll take that to heart!
...I only wish the bank acct would support your most sage advice

Edward

 

Me too!

The answer is always easy....implementation, not so easy.

 

Castrol SRF... I won't even consider using anything else.