How long may I use brake fluid after opening it?

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673
Location
Washington State, U.S.
I was going to flush my brakes on my 20 year old car today because the reservoir had gotten a bit low since I last flushed them 6 years ago. I got one corner complete, but realized it was late in the day, I was tired, and I was losing light. Therefore, I'm going to do all four tomorrow or the next day. Do you think I need to re-purchase fluid? I know it's always emphasized new fluid is important, but would 24-48 hours after opening, with the cap tightly on, be a problem? Only about 1/4 of the fluid is missing from the container. Thanks!
 
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Messages
13,380
Location
ROCHESTER, NY
That isn't a problem at all, just keep the cap on snug! Think about how long the fluid is in your reservoir! Yes, the reservoir is sealed but, look at what the reservoir is exposed to with outside & underhood temps which also expose the res to moisture.
 
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18,187
Location
NH
Ditto. I don't think I would worry about one year old open container, the cap is likely sealed better than the reservoir. Maybe store in the house, where temp and humidity does not fluctuate as much as the basement or shed.
 
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2,630
Location
Montreal, QC, Canada
I keep it for the initial bleed at the first wheel if it is older fluid. Then when it is running clean right at the bleeder I start adding brand new unopened fluid. That way you don't waste fluid diluting the gunk in the MC.
 
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838
Location
One Step Beyond
I would be more worried about the current fluid being 6 years old than continuing the next day with an opened bottle (from previous day). Brake fluid opened the day before should be fine (with cap on bottle). I flush my brake fluid every 2 years. I always have a 'new' bottle of brake fluid (stored in basement) inside a plastic bag with a 'rechargable' desicant. Does it help ? ? ? ...... Can't hurt.
 
Messages
4,253
Location
Central Maryland
Originally Posted By: Ayrton
I was going to flush my brakes on my 20 year old car today because the reservoir had gotten a bit low since I last flushed them 6 years ago.
Your fluid level is probably low because your pads/shoes are worn, and the hydraulics have compensated. Nonetheless it's time to bleed the fluid, which is probably moisture laden.
Originally Posted By: Ayrton
I got one corner complete, but realized it was late in the day, I was tired, and I was losing light. Therefore, I'm going to do all four tomorrow or the next day. Do you think I need to re-purchase fluid? I know it's always emphasized new fluid is important, but would 24-48 hours after opening, with the cap tightly on, be a problem? Only about 1/4 of the fluid is missing from the container. Thanks!
One day is no big deal.
 
Messages
9,614
Location
Pennsylbammyvania
Originally Posted By: larryinnewyork
I always have a 'new' bottle of brake fluid (stored in basement) inside a plastic bag with a 'rechargable' desicant. Does it help ? ? ? ...... Can't hurt.
^^^This is the ONLY way I will store either opened, or a sealed bottle/can of brake fluid, but since my basement is humid, I keep it in my room, or the front of the garage. wink
 
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