Goin thru my cabinet in the shop the other day and I came across a couple of bottles of partially full brake fluid clean and unused. I opened them at some point, God knows when and then forgot about them. Are they still good? Does it have a shelf life?
Brake fluid is very hygroscopic. I never keep after open. I don't really even like old unopen bottles..except Silicone based even avoid that. My older systems I just get smallest size and use and recycle back to Auto Parts store.. Store is 5 minutes away.. Cheap stuff.. risk is not worth it..
Brake fluid being hygroscopic by nature, my first answer would be No, toss it. Buy new. If it's as old as you say, it's probably an inferior brew compared to the newer fluids on the market. Aint worth getting it wrong.
it doesnt expire once you put it in the car. whats the difference. as long as it was in a sealed container use it.
no offence here but you've been mis informed here, it does expire and it is still hydroscopic in your deceivingly sealed master cylinder reservoir, nothing last for ever, it should be changed just like your oil needs to be changed, it degraduates over time and ive been told atleast every 2 years change time regardless of how much its driven! another point here brake fluid does cop a fair amount of heat through the braking system especially on longer trips or heavy braking why would you use old stuff when its so cheap to buy a new bottle, here in oz its 6 bucks a bottle , its cheap its easy to bleed brakes, and its good reassurance, lets remember this is what helps your car stop and not hit whats in front of your pride and joy
If the container it came in is plastic and you have not used it within the past ~6 months. Toss it. As mentioned brake fluid is hygroscopic and will absorb moisture from the air. Plastic bottle containers are not fully sealed. As for brake fluid in the car. Bleed it and replace it every two years. The boiling point dramatically drops with in the first year. I still find it surprising how many people get paranoid about engine oil and change it every 3K miles, yet have the same brake fluid from the factory
Brake fluid over time will attract water, when I used to help out at a local lube/brakes/muffler shop we had a neat little gizmo that you could put in your brake master cylinder to see how much water content was in the customers brake fluid and whether it was good or not. Its like anything liquid in a car eventually its going to need changing, some more often then others.
If you're really cheap, just heat it to above 212ºF and boil off the water. Nothing left in the pot but pure brake fluid. Bob
Actually is does "expire" in the car. When you put it in it is either very light in color or clear and then it becomes very dark with time. It is water fouled when it becomes dark. We change our oil and some of us even change the fluids in out gear boxes or transmissions. Brake fluid should also be changed periodically. You open the bleeders and flush the system. Bleeding is the back yard way to do it or if you look on this thread: http://www.jalopyjournal.com/forum/showthread.php?p=7531745 you will find a real home brewed way to build a tool to flush the system and belld the brakes in one fell swoop.
And DOT 3 and 4 interchange with each other but not DOT 5 as it is a silicone base, now, with that said, there is a new kid on the block, DOT 5.1 which is interchangeable with DOT 3 and 4 as it is a higher boilong point and less water absorbing then the others. And yes, all has a shelf life, most companies recommend disposale after 90 days of opening a bottle. As I get older I mark the date with a sharpie items in my shop just to remember these days!
I'm not sure that it is going to break down in a tightly sealed plastic bottle over a year or so but when I went to a brake clinic put on by a EIS factory rep from NAPA a few years ago he did say not to buy larger containers than you could use up in a reasonable amount of time and do not leave them sit open. At the time he said one of the big culprits was these pump setups that went in the tops of gallon cans of brake fluid that were really popular in shops and service stations. He said that was pretty much like letting the jug sit open on the bench drawing moisture. I'm like the others in that I only buy the size container that I need at the time and don't keep the brake fluid around very long. Unless you are doing a lot of brake jobs all the time there isn't a need to buy large containers of it to keep on the shelf.
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