Brake fluid shelf life?

[autobonrun]

I'm preparing to rebuild the calipers and change the hoses on the rear of my 79. The brake fluid I have has probably been on the shelf for a year. I only used about half the last time. I'm curious given the hygroscopic nature of brake fluid, will it keep on the shelf without absorbing moisture. The cap is on tight but it's only a plastic top on a plastic container. I'm thinking mositure could enter past the threads. In the future, should I always start with a new bottle and just discard any unused fluid? I don't want to be wasteful, on the other hand, this is not the time to get cheap either.

[MrKJBlue]

Everything i've read about brake fluid and my gut feeling says dump. All that work rebuilding the calipers.. as you say not the time to get cheap.

[Joeaksa]

As long as its a fresh can, never opened and not exposed to the atmosphere, I would keep it for a few years at a minimum.

If you are racing or doing autox or DE then you are going to be using it more often anyway but for normal use would not have a problem using it out of a freshly opened container. We use hyd fluid for airplanes that is 10 or 15 years old as long as its not been opened and there are no limits stated on its container or the books.

Joe

[911pcars]

While brake fluid is hydraulic fluid, hydraulic fluid does not have the same properties as brake fluid. BF must meet certain DOT specs when used in a brake system. Hydraulic fluid, the type used to control car lifts and floor jacks, even ATF, operate under different, less arduous conditions.

The shelf life of an unsealed can of BF is the same as in your brake system. Thus, you should dispose of it the same time you change your fluid. In other words, its properties, in an opened can or in your system gradually go downhill as it absorbs moisture from the air.

Sherwood Lee
http://members.rennlist.org/911pcars

[RoninLB]

Originally posted by 911pcars
gradually go downhill as it absorbs moisture from the air.

Sherwood Lee
http://members.rennlist.org/911pcars

I wonder if you could heat up unused fluid before using it, technically asking.. I would think H2O would be released/logically thinking

[911pcars]

Ron,
That's an interesting idea. Heat the brake fluid to >212ºF to rejuvenate it. Sounds feasible.

Sherwood

[RoninLB]

Originally posted by 911pcars
Sounds feasible.

sounds good to me to.. like what if you had 3/4gallon of irreplacable ATE Super Blue lying around

[Noel]

I bought about 8 cans of ATE Superblue when I heard that the DOT had banned it. I would imagine that the shelf life is longer if it is in a never opened metal can though.

[RickM]

Half used, previously opened container....temperature extremes in garage. I probably would not use on my P-car. But I'd probably use it on a beater car.

[Porschedude]

Boiling your 1/2 used can of Brake Fluid is like putting a Car Alarm in a Yugo. But one must ask one self…Is it really worth the effort?

In my business, we back fill expensive fluids with a blanket of gaseous nitrogen or helium to prevent both interaction and contamination.

[RoninLB]

Originally posted by Porschedude
But one must ask one self…Is it really worth the effort?

the intellectual question was "heat up unused fluid"...

so far no hard answers.. and that nitrogen is great for freezing bearing races before install... better than freon..

[Jdub]

Though it is not economically a good idea, I purchase the smaller cans of brake fluid and, if I must keep 1/2 a can around, double wrap the opening with plastic and then screw the cap on tight.

John

[Oldporsche]

I've been toying with the idea of a "seal-a-meal" for vacuum packaging of things like this.

I do like the idea of backfilling with Nitrogen. I could do this from the Heliarc tank.

Good luck,
David Duffield

[jthwan22]

You can always use the half can on the start of the big flushing job.

[Porschedude]

Originally posted by RoninLB
the intellectual question was "heat up unused fluid"...

so far no hard answers.. and that nitrogen is great for freezing bearing races before install... better than freon..

RoninLB
What makes you think that the water is going to be released at the boiling point of water? Compounds change the boiling point of each of the elements within the compound. Taking the brake fluid to the New Rated Value, "475 F", of the fluid would be the minimum temp, "Boiling Point", I would use to distill the water out of the brake fluid. Since this is what one is trying to prevent "Boiling or Out gassing of Water in the brake system"

Make sense?

Keith

[speeder]

OK, I'm no brake fluid expert, but I took a class in college many years ago called "logic", and once again it has risen up and interfered with my enjoyment of reading the Pelican board. Here are the reasons:

1) If brake fluid is *that* hydroscopic, or alternately if a *small* amount of moisture in fluid has a disasterous effect on braking, HTF does any car on the road stop?? Care to hazard a guess what the % is of cars that have EVER had their brake fluid changed? Or the % of people who are aware that you are supposed to have it flushed/changed? (I vote for under 1% on both).

2) I do realize that brake fluid is hydroscopic and that moisture will cause corrosion of internal parts and in larger quantities will degrade braking ability, (especially in track situations where brakes get very hot), but B.F. also gives plenty of visual clues when it gets contaminated or old, at least in the car. Are you guys suggesting that in the can it could look pristine but be garbage? Just asking.

I am in the 1% of motorists that actually changes my B.F. regularly, I like it clean, but have never given a second thought to using fluid from a previously opened container, as long as it is visually perfect. You guys are making me afraid to ever open my resevoir cap again on the car to add fluid, should this only be done in a special zero humidity chamber? Just wondering.

[derkpitt]

Shelf Life = The time a unused material can sit on the shelf by manufacture recommendation.

We always follow the manufacture recommendation.

[RickM]

Denis, you make some very good points. I guess using relatively new BF is fine. I know from my own experience that BF cans can sit around a garage for a LONNNG time before being reused. I am curious if there is a shelf life for previously opened BF. What does the average labeling say regarding reuse?

[Wil Ferch]

Ahhh...Speeder and others.....

I think you mean "hygroscopic" ??......not "hydroscopic"?

But seriously, you're correct..it takes only a small amount of water contamination...something on the order of 1-3%...to reduce brake fluid boiling points something like 30-40%.

---Wil Ferch
(pedantic as ever)

[911pcars]

Denis,
I think the guys here are thinking more about brake fade due to moisture boiling during sustained, aggressive braking. For 95% of the driving population/situations, moisture damage is more of a factor than brake fade. We have a large number of franchise repair shops (Pep Boys, Sears, etc.) that derive most of their income from brake-related repairs.

What if I just use 4 oz. from a container of Castrol SRF and I've just spent (for the life of me why?) $70 for it? Do I dump it and consider it part of my fantasy racing budget? Shelve it and relabel as "expensive flushing fluid"? Is there an alternative? Can I purchase nitrogen or some other inert gas in small quantities to keep this fluid warm and fuzzy?

If one uses new fluid from a previously opened can, you should be aware of the wet boiling specs on the label as the wet spec is now applicable to your system. For example:
Valvoline Synpower, a DOT 4 spec fluid: dry BP = 502ºF (261ºC), wet BP = 343ºF (173ºC)
Whereas the spec for Dot 3 fluid is (dry BP = 401°F, wet BP = 284°F)

In other words, a "wet" DOT 4 fluid does not even reach the min. specs for fresh DOT 3 fluid.

I believe the term is "hygroscopic".

I gotta go change some BF,
Sherwood
Brake Fluid Chart