Does brake fluid have a shef life as I opened a new bottle 6-7 months ago and its sat in the garage since I think it was castrol if that makes any difference? If I need to replace it, any recommended brands? Cheers
brake fluid absorbs moisture ,that is why when new it has the foil seal under the lid to stop contamination and why it is supposed to be changed every couple of years.
I think you are supposed to use it up within a month. But check the info on the bottle itself. I would say if you have to store it, then the airing cupboard would be the best place (in the uk of course!)
For the price of fluid I don't store it but don't have more than 1/2 litre bottles anyway so there's minimum wasted. Its not the most economical way but there's little doubt about it. If its opened then a month should be OK. If you have it in a large bottle, say 2 litres, your local garage probably has a moisture tester you could check it with. Accelerating is easy, its always the stopping that causes problems.
When you only have to change it every two years in a hard working braking system, where I believe it's the heat that makes it hygroscopic, I'm guessing as long as you don't shake it and introduce bubbles into it it should have a shelf life of at least two years. Could be wrong of course, it has been known!
I don't want to bog down a simple question with too much detail but as you say its hygroscopic and will absorb a certain amount of moisture from the atmosphere just being open to it. A brake system isn't truly sealed at the master cylinder cap because it has to allow for fluid movement as the pads wear or cylinders move. What the manufacturers are suggesting as a 2 year fluid change is that by then it will have absorbed sufficient moisture to alter the boiling point of the fluid. The fluid boils at the face of the caliper piston and creates a gas, this gas is compressible and leads to greater travel of the master cylinder which most people call fade. Fade is actually the temperature at which the friction is no longer available. It is not good practice to store fluid in a bottle for those sort of periods although you could well use it to the limits of your personal driving with no problems at all. I was just making the point that compared to the price to have fresh fluid in a high performance car or bike against the possibility of some level of failure wasn't really justified. That's why I only have small bottles and keep any others sealed until used. In the whole of a bike system is probably 1/2litre. DOT4 is best. Manufacturers spec is gospel. If you have a hard working brake system, high loads/temps/environment then service intervals are shortened. Racers change it every meeting. The option is to fit silicone brake fluid which doesn't absorb moisture, like the military do because of long storage periods, but last time I had some it was 200 quid a gallon,50 quid a litre. Silicone is no use in cold weather because it thickens up. Of cause, if you have an ABS Blade you have the nightmare of bleeding it!! If its going in the clutch hydraulics then no problem.
