It's sat on the shed shelf for about 12months (opened but in a container) – I seem to remember reading it can absorb water and doesn't last? Is that right?

If it's got a lid on it that's tight it will be fine

If it's been opened, my inclination would be to buy a new bottle. It isn't expensive, it is inclined to absorb water once opened, and for the cost of a new bottle I'd just bin the old stuff safely and got with fresh.

Does the bottle itself not give any indication of shelf life?

I'd imagine it will be ok I have a bottle I've been using for about a year and brake performance hasn't been noticeably affected by it. I'm guessing it must last a little while as the particular brand I bought sells it in 1 litre bottles and I'm only half way through after bleeding my brakes every couple of weeks.

Iain

No limit on shelf life of DOT brake fluid as long as the lid is on securely. IE airtight. If there is any doubt about it, chuck it and get new. Get 5.1. Still cheap but added peace of mind.

It's your brakes. Just buy new. You should be looking to replace it annually on your bike (and car) anyway due to water absorption. If it has been opened and not in a truly airtight container then I'd just not risk it.

As for unopened bottles… I have one in the garage but it gives no indication of date of manufacture so I've no idea of its age. I've had it for a year but it could have stood in a warehouse for decades for all I know.

Why not try it and see – if the performace is bad then re-bleed with a new bottl. IME if there is 1/2 bottle left and the lid is on tight then I have no issue in using an old bottle (although 5 years is pushing it 😉 )

The worst that can happen is its absorbed moisture, and you boil the brake fluid on a big descent. You've got two brakes so its not the end of the world. As long as the cap has been on tight it should be fine.

My car workshop (a local independent VW/Audi specialist) has something to test fluid to see if it needs replacing (saving me the cost of unnecessary work as indicated on the service schedule). Anyone know how that works?

Obviously for the small quantities for bikes, just buy fresh when you need it. But how do you get rid of the unwanted stuff? Oil recycling at local dump?

It will be fine, I would be more worried about how long its been in your cars system without a 2nd thought..

its fine .if you had left it for a year with no top on then i would be concerned.
in all the years ive had cars i have reguarly changed all brake fliud in the lines and done the same on customers and ive never seen an improvement or poor performance due to fluid being "old"
i think you really have to be a donut and let it get expeosed to huge amounts of airborne moisture to have a problem.
if it was my car with my family in id be more concerened than on a bike.

having said that its dead cheap

I'd use it.
In fact, if anyone has got any 12 month old brake fluid that has been stored in a sealed container, I'll have it to save you the disposal cost. 😉

optical refractometer

I've had a big can of 5.1 for about 4 years now. Just kept with the lid on tight. It's still absolutely fine.

n.b.

For those of you spouting that 5.1 is 'better' and how you are gods gift to mechanics because you bleed your brakes with a fresh bottle of 5.1 every other week?

You do know why 5.1 is 'better' dont you?

So why bother replacing it so often?

For the rest of you………..

DOT3, DOT4 & DOT5.1 are all basicaly the same chemicals, but with varying levels of addatives to keep the boiling point consistent as they absorb water. The side effect of these addatives is to drop the boiling point of the 'dry' fluid. So if you do in fact change the fluid every 5 minutes, you'd be better off with a good quality (yes not all brake fluid is created equal) DOT4. The DOT standards are a minimum the fluid has to meet. So yes DOT4's standard is a lower boiling temperature, but a good quality DOT 4 will be significantly higher when dry, it just drops off quicker as it absorbs moisture from the air.

You should be looking to replace it annually on your bike (and car) anyway due to water absorption

I bet car mechanics think christmas comes early every time you go to see them… unless you're doing it yourself.

Thisisnotaspoon – I agree with you and have used 4 and 5.1 but you have to be careful as some manufacturers state that a certain one has to be used so as not to invalidate the warranty.