Once it has been opened, how long a shelf life does brake fluid have in an unheated garage?
DoT 4 shelf life
- Thread starter ShakeyGS
- Start date
AberdeenAngus
Registered user
If it’s in a well sealed container....indefinitely.
I tend to be thinking along the same lines as Wobbly. I don’t think that just screwing the lid back on constitutes resealing the bottle.
Let’s over-think this.
If I open the bottle and use some fluid then that volume is replaced by air. In Scotland that air is likely to be humid so over the next year or so I think it’s possible for the fluid to take up some of that moisture.
At present, after cleaning up my brake calipers as part of my annual service, I’m struggling to get a good feel at the lever. My bottle is about 3 years old so I have ordered some fresh stuff just to eliminate my moisture theory.
Also, it gives me something to do whilst shielding
Let’s over-think this.
If I open the bottle and use some fluid then that volume is replaced by air. In Scotland that air is likely to be humid so over the next year or so I think it’s possible for the fluid to take up some of that moisture.
At present, after cleaning up my brake calipers as part of my annual service, I’m struggling to get a good feel at the lever. My bottle is about 3 years old so I have ordered some fresh stuff just to eliminate my moisture theory.
Also, it gives me something to do whilst shielding
I put six month old brake fluid in my car, it had been resealed and left in my shed. Tested it with my brake fluid tester beforehand and it came up all good, as new. I think there's a lot of perfectly good brake fluid been chucked away.
Sent from my MI 8 using Tapatalk
Sent from my MI 8 using Tapatalk
I try to buy as little brake fluid as possible, my local recycling centres won't take it 
I use something like this https://www.ffx.co.uk/tools/product...8DLn5MnLNRRRk2dUuNoObgRnEh31HEghoCCZQQAvD_BwE. Mine looks identical but doesn't have the Sealey badge so was half the price.
Sent from my MI 8 using Tapatalk
Sent from my MI 8 using Tapatalk
Interesting. I didn’t know you could test it.
I have a 5 litre container for, ahem, old engine oil which I empty into the big container at the centre.I try to buy as little brake fluid as possible, my local recycling centres won't take it
Thanks for that.
AberdeenAngus
Registered user
Because its wasteful.
But lets look at the numbers....
At 20 degrees C, a cubic metre of air can hold a maximum of 18 grams of water at a relative humidity of 100 percent.
Take your average brake fluid container of capacity ½ litre.
Let’s assume its half full so ¼ litre of air.
That’s 1/4000 of a cubic meter, so approx. 0.0045 grams of water.
Specific gravity of DOT4 is 1.07 therefore ¼ litre x 1.07 = 267.5 grams
So in the bottle you have 267.5 grams of brake fluid and 0.0045 grams of water.
Lets assume all that water is absorbed by the remaining ¼ litre of brake fluid.
Therefore the ratio of water in brake fluid is 0.0045 / 267.5 = 1.6x10-5 (i.e. 16 parts per million)
Moisture in brake fluid only starts to cause problem when you get above the 1% range i.e. 10,000 ppm.
I think you’ll be fine.
I didn't get that first time , can you just go through it again ?
But the BMW service manual says to always use fresh fluid from a sealed container 
OK so at max 16ppm I’ll just try the technique from the manual using my current fluid. Thanks for the information.
OK so at max 16ppm I’ll just try the technique from the manual using my current fluid. Thanks for the information.
Agree completely.
I beleive brake fluid should be tested rather than simply replaced.
Whenever I've tested it for water content it's always been well within tolerance.
If it contained any moisture, the pedal would be spongy and get worse the more the brakes were used.
I got one from ebay that the size of a cigar case , it has two probes on the end to test the fluid for moisture content.
I too struggled to get firm pressure following new brake lines/fresh fluid. Tying back the brake lever for a couple of days firmed up the lever well.....
At present, after cleaning up my brake calipers as part of my annual service, I’m struggling to get a good feel at the lever......
I’ve been doing that as well but to no avail this time
Water will make no difference when cold, it will only become apparent when it reaches boiling point (higher than 100deg. C because it will be under pressure) and becomes vapour, which is compressible.
Similar threads
- Locked
