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#4634825 - 01/14/18 03:57 PM Open Brake Fluid
coopns Offline


Registered: 02/16/05
Posts: 786
Loc: Scituate MA
I opened and used brake fluid container (removed fluid and filled).

Can I use again? I thought I remember someone saying it is (yeah, big word of the day...had to look it up) hygroscopic - absorbs moisture but would that apply even with cap on?
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#4634849 - 01/14/18 04:22 PM Re: Open Brake Fluid [Re: coopns]
Trav Offline


Registered: 11/20/06
Posts: 18272
Loc: MA, Mittelfranken.de
Sure you can, put the cap on tight and keep it in a dry cool place, putting it in a ziplock bag is not a bad idea if its going to be longer than a few months.
Unless you live in a very dry climate like southern CA, NM or AZ, etc I would toss it at the 2 year mark.
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#4634865 - 01/14/18 04:40 PM Re: Open Brake Fluid [Re: coopns]
DBMaster Offline


Registered: 09/18/12
Posts: 5280
Loc: DFW
I don't know how accurate the electronic brake fluid moisture detectors are but I tested the fluid in a plastic bottle that had been opened and re-capped for over four years and it still tested as being fine. I've never even thought about it in the past (my pre-BITOG days) and haven't had issues yet.

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#4634962 - 01/14/18 06:06 PM Re: Open Brake Fluid [Re: coopns]
slacktide_bitog Offline


Registered: 03/20/08
Posts: 5867
Loc: USA
chuck it, especially if it's a plastic bottle.

If it's a metal can, it will probably be OK.

If you're just using cheap DOT 3, you can get a new bottle of that anywhere. Now if iot was something more premium and expensive, then I could see the point of using the remainder.

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#4634975 - 01/14/18 06:20 PM Re: Open Brake Fluid [Re: coopns]
JLawrence08648 Offline


Registered: 01/20/17
Posts: 166
Loc: NJ
Once the cap is off, it pulls moisture from the open space in the bottle. I wouldn't worry about it, it's more important to change your fluid then worry about a little bit of moisture in the air in the bottle.

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#4634977 - 01/14/18 06:22 PM Re: Open Brake Fluid [Re: coopns]
bdcardinal Offline


Registered: 06/03/05
Posts: 10815
Loc: Santa Barbara, CA
Even in a low humidity environment unless we are talking a bottle of Castrol SRF, brake fluid is so cheap it isn't worth saving opened bottles.
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#4635122 - 01/14/18 08:25 PM Re: Open Brake Fluid [Re: coopns]
eljefino Offline


Registered: 06/15/03
Posts: 32391
Loc: ME
A half full bottle in a garage is better than a vented master cylinder in a car driving in weather and seeing heat cycles.

If the fluid's still clear/ amber, run it. At worst use it as a pre-flush when bleeding then finish with something new.

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#4635243 - 01/14/18 11:01 PM Re: Open Brake Fluid [Re: coopns]
andyd Offline


Registered: 09/25/04
Posts: 6894
Loc: Marshfield , MA
Wet brake fluid is better than no BF in a pinch, As long as it didn't freeze, it would be fine in a Hydraulic clutch. Also you could squish the bottle until the level was up even and put the top on. I use left over BF to set up airlocks when I bleed.
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#4635351 - 01/15/18 04:17 AM Re: Open Brake Fluid [Re: coopns]
Lubener Offline


Registered: 01/22/11
Posts: 2508
Loc: N.Ohio
I have used previously opened (2-3 years) bottles of brake fluid and never had a problem. As long as it is tightly sealed, I wouldn't worry.
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#4635876 - 01/15/18 03:23 PM Re: Open Brake Fluid [Re: coopns]
barryh Offline


Registered: 01/09/16
Posts: 296
Loc: Cheshire, England
The way I look at it is the fluid in your car is vented to atmosphere via the reservoir cap. The fluid in your bottle or tin is sealed. Which is going to deteriorate quicker ?

The whole thing about throwing unused brake fluid away once opened is ridiculous. If it lasts 2 years in a car that regularly sees 99% relative humidity it's going to last more than 2 years in the tin on the shelf in my dry garage. I would and did choose a tin container over a plastic bottle.
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1979 BMW R45 (Triple QX 5W40)
2009 Mercedes C180K (Shell Helix Ultra 5W40)

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