911 Rod

When opened and then closed with 3/4 used,
is the fluid still good 6 months later?
After flushing in the fall, I want to bleed without getting a new can of blue just to use a couple of ounces.
Thanks

g-50cab

Throw it away.. it absorbs water..

theiceman

If it is well sealed it should not should it ? the one thing I liked about the blue is that it resealed really well, and poured really well,looked like some thought had gone into the packaging as well as the product.

KC911

Although some might disagree, I do that. While it is true that an opened can might absorb 'some' moisture, imo it will be no worse than fluid that's in your MC resevoir that is exposed to air (via the overflow tube). That being said, I do use an unopened can for the flush.

Keith
'88 CE coupe

911 Rod

Now you know why I asked.
If I did use it. The so called "moisture" would be in my resevoir anyway.
No?

KC911

Imo, the answer is yes, and it is insignificant. I recently did a bleed, and probably didn't add more than a couple of ounces to the resevoir. In theory, everyone that says the opened can will absorb moisture is absolutely correct... in practicality, I just don't think it matters for a couple of ounces that's been on the shelf for only 6 months...and I'm a cheap b**tard !

Keith

theiceman

I am no expert and I am sure there are lots of guys here that would disagree with me , But I think I would be way ahead if i were to even suck that stuff with a syringe out of my reservior and put in some super blue sealed in it's container even after cracking it 6 months ago.

On a somewhat related note I used to remember brake reservoirs having a rubber diaphragm on top on other cars. It would stop moisture entering the reservior and the diaphram would collapse with the fluid displacement on brake pad wear. don't remember ever seeing anything like that on my Porsche. Are they really open to atmosphere ?

KC911

If you ever forget to clamp the overflow tube while using a power bleeder, you will find out for sure ! ...I've never done that, but plenty of others have....

Keith

911 Rod

I would think the fluid in the reservoir would be in the exact same condition as the open can. They sat literally 3 feet apart all winter.

theiceman

Would also explain why you are suppose to flush it every 2 years. .. ( the reservoir .. not the open can )

Edward

Brake fluid is, as others have mentioned, hygroscopic ...absorbs moisture. But this trait compounds over time and exposure. While I would have no qualms using 6-month-old fluid in a closed can for topping up, I would not do a full flush with this fluid and then go to the track. It's a matter of degree: how much are you willing to expose yourself and your most critical safety system to a potential malady. So while a 6-mos closed can poses no great risk to a street car's brakes in a good state of tune, be aware that under more stressful conditions where the brakes are taxed to their limits, the freshest fluid of highest wet boiling point is critical.

So why flush at two years? Because as the fluid absorbs moisture over time, it's percentage of water content increases. The result is wet boiling temp decreases, boiling fluid creates air bubbles in the system, and air compresses whereas a fluid does not: spongy pedal at best ...pedal to the floor not stopping at worst. Moreover, the water content can corrode brake components. So yes, flushing the brake fluid is important preventative maintenance for any car, and high-performance ones that are driven fast and braked hard even more important. Hope this helps.

Edward

911 Rod

Thanks for you input Edward.
Actually I'm bleeding my brakes for the track.
Correct me if I'm wrong.
The fluid will boil closest to the brakes. Hence the need to bleed.
Topping up is the farthest point away, which is where the "out of the can" fluid will be.

Steve Weiner-Rennsport Systems

"Brother" Edward offered some VERY good advice,......

Not long ago, I borrowed a brake fluid tester made by Leitz (the camera people) that tests the moisture level of glycol-based brake fluids and tells you its boiling points. Damned expensive instrument to purchase so I never stepped up and bought the thing. For me, it was FAR cheaper to simply flush & bleed my customer's cars on a regular basis to prevent corrosion and brake failures at the track.

Nevertheless, it was quite educational to see precisely how quickly these fluids absorb moisture once exposed to the atmosphere and watch the boiling temperatures go down. Personally, I would never, ever use any brake fluid thats been opened for more than 2 months. This might be OK in somewhere in a desert climate but IMHO, not where the humidity levels climb beyond 30-40% at any time of year.

Frankly, brake fluid is pretty darned cheap overall and must be considered as a consumable, just like gasoline,... Its FAR less expensive than replacing corroded caliper pistons and/or torn up body work from boiled fluid at a track event.

KC911

Steve, You are without a doubt 'the man' (amongst others) when it comes to these cars, but please explain how the partial can (sitting on the shelf for 6 months) is any worse than the fluid that's in the reservoir (that's also exposed to air)? I'm not arguing with your wisdom & experience (that'd be dumb )....I just don't understand. To repeat, I would never use a can of opened fluid for a flush/change, but I just don't see the issue with adding a couple of ounces during a bleed as long as you are flushing & changing to 'new' fluid at the recommended intervals?

Keith

ps: Steve, have you ever used your tester to compare an opened can with the fluid that's in the resevior (from the same can)? I'd be curious....

Edward

Dang, Steve, thanks for the kind words! ...from YOU that's quite a compliment!

Rod and Keith,

I don't know the physics to fluid dynamics, but even though the system is "linear" and not recirculating, there is still some mixing, especially from the heated fluid around the calipers interacting with the cooler fluid up the pike. So the grand questions are: how much mixing is there, how much would that mixing decrease the wet-boiling point, and how much such a decrease would translate into a loss of braking potential? I think these are noteworthy concerns worth finding out, and hope someone does one day soon. But the answer for me right now is I would simply not take that chance, especially given the potentially disasterous results should the "experiment" fail at the track. There are some things I will cut cost on, like using tape for numbers instead of a cool magnetic deal. But on brakes? I guess I'm just going to be a "stickler" on that one.

Edward