How long can brake fluid sit in the can?
 

Hello!

I have some Pentosin DOT 4 that's been in the can on the shelf for let's say 6 or 7 years.

The can was mostly full and I'm in dry Colorado.

It "seems" fine and looks way better than what I'm replacing lol. Looks like very weak iced tea.

What say you? Thanks

There will be two schools of thought on this. Any brake fluid opened, sat in garage, 1 year and it goes into the trash. Or it’ll be fine in your commuter car, just use it.

Put it into a desiccator next time. For even race applications, a sealed lid on an open container will contain negligible amounts of water. A deuterated solvent used for nmr, not so much. lol

Standard wisdom is that once you’ve opened it to the air, two years. No different can vs brake system.

BF's downfall is it's propensity to absorb water through moisture in the air. When this happens it turns the BF into a mushy nasty looking material. If your fluid still looks clear you're probably OK.

That said - considering BF is still fairly reasonable in cost - not sure I would use it in anything you really care about.

Thank you

It's bike stuff so I'll probably buy a new can and start over, should take 10 minutes lol.

The reservoir looked pretty nasty but is ok now after some TLC.

Instead of guessing whether brake fluid is contaminated with moisture or not, just invest in a cheap electronic tester from your favorite big box store on the internet. Then you don’t need to throw away good fluid or depend on some stranger’s opinion. As a bonus, you can also use it on the fluid that’s in your vehicle to tell whether you need to change it!

And while fluid that looks nasty is obviously contaminated, it’s not true at all that clear looking fluid is ok or that you can tell by appearance. I do this almost every day.

Thanks Denis! I do have the tester and it didn't mind my can of fluid 0% i just had a consummate thirst for all the knowledge. :)

Thank You ... I need one now ;)!

This has been a constant question for me as an MC owner. I use so little fluid when I bleed the system that easily 70% of the bottle contents end up sitting on the shelf.

I have a couple of unopened cans of ATE "Super Blue" from the early 2000s sitting around, I'll accept bets that they test zero moisture when I open them some day. I'll video the whole thing. :)

There are so many wive's tales about the fluids and lubricants we have in our machinery. My favorite, (or least favorite), is that oil goes bad in the crankcase when a car is parked for a long time. Or that seals dry out in the engine from sitting. All parroted on the internet by people who have never revived a long sleeping engine or disassembled an engine, etc. It is true that gasoline goes bad in an ugly way from long time sitting.

Heat and stress kills seals, period. Not bathing in oil for years. There is a film of oil on even the top end of an engine that has sat for years. The front pulley seal on my F-250 Power Stroke just started leaking, that is a vehicle that does road trips pulling a trailer. I'll change it, no big deal. Seals are important, don't get me wrong. So is dry brake fluid but getting a tester was a game changer for me. No more guessing. :cool:

I'm the other school of thought. Open brake fluid can, use what's needed, throw rest away. Zero open shelf time.

I am with Guy.

How much is a bottle of brake fluid, pretty cheap

I have a few cans also. Thanks for the link to the tester, I didn't know such a thing existed.

In an unopened undamaged container, it would last practically indefinitely

As a counterpoint, there are probably millions of old cars on the road with working brakes that still have original fluid. So we are probably overthinking it.:)

^^^ My 2001 F150 had the original brake fluid when I traded it for my 2014 F150. 🤯 But, I changed the brake fluid in my track car every event. So probably 6 - 8 times a year.

I’ve changed the brake fluid in my 2014 F150 several times

Why guess, an e-brake fluid hygrometer costs <$25 and will tell you whether the fluid is still good or not.

I agree! Why read the thread? Just go to the bottom and fire away.

:p