Brake Fluid - will it 'go off'?

[Ronin 09]

Good morning,

I know that brake fluid is hydroscopic, but what I need to know is whether it will absorb water while in the bottle (ie. Go off) or only in use under pressure…

Reason is, I have a 2/3 full bottle of Motul 5.1 and it has been open for about a 2 years… will it still be OK to do a flush of my system, or should I can it and just get some more? The container has been indoors and sealed since it was opened…

Cheers

[Snowman]

Marcus - I recently ask Benno the same question as I have a half bottle of Castrol SRF and someone (aka Roy) told me it would go off. Ben however tells me as long as the bottle was re-sealed properly then it will be fine to use.

[Ronin 09]

excellent... I actually have two bottles of 2/3 full brake fluid :confused: , one of which is less than a year old. Hopefully that will get me through a brake / clutch flush (braided lines install)

Thanks Andrew

[MANWHORE]

it goes off when it is exposed to water. when you say the bottle is open, I asusme you mean, you've opened it, but put the lid back on tight. It should be fine.

[Ronin 09]

it goes off when it is exposed to water. when you say the bottle is open, I asusme you mean, you've opened it, but put the lid back on tight. It should be fine.

yep. lid been on thanks

[Roy]

Marcus - I recently ask Benno the same question as I have a half bottle of Castrol SRF and someone (aka Roy) told me it would go off. Ben however tells me as long as the bottle was re-sealed properly then it will be fine to use.

lol...Castrol SRF comes in a metal tin, other fluids such as my old AP fluid came in plastic containers, and if not stored in a cool dry place can absorb moisture thru the plastic packaging...not likely to happen if you are running the Castrol:)

The Motul i bought recently is in a plastic container, and i would be wary of using it after 2 years if it hadnt been sealed properly and stored in a cool dry place.

Also another reason why the Castrol SRF may not be a good example is that Castrol claim that the silicon ester technology used for the SRF is less hygroscopic than other simialr race fluids

Castrol aslo claim that the SRF reacts chemically with the absorbed water preventing the fluid's high temperature performance from deteriorating as rapidly as other fluids. This seems to go against the general trend that the more suitable for race applciations the fluid, the more hygroscopic they generally are.

Had to dig this up on my PC...but the reason Motul claim they get away with the use of plastic containers is they are filled with Nitrogen to increase shelf life and eliminate contamination while factory sealed. Though they make a point of saying factory sealed. In frequent Q&As i did read that once opened Motul recommend using the whole container...or as a minimum sealign tightly and storing in a cool, dark, dry place

Thats only what i have read, but its from the manufacturers so:confused:

[The Dan]

It can go off. usually takes 2 years or so but as long as it is perfectly sealed then you shouldn't have a problem. If you are in doubt. You can take it into pretty much any Midas or ABS store and they have hydroscopes that can tell you the condition of the fluid...ie..the boiling point of it.

[nuffin_werks]

ok , i live in a high humidity climate, and it's recommended that brake fluid gets changed 6 monthly... now we also respect that different containers have different moisture preventing qualities... i recommend you only get enough fluid to do your service, and never use an open bottle that is more than a few weeks old , as you cant garrenty the seal quality....

anyway i found this info doing a google search :

[/color]

Brake Fluids

Thanks to Dave Zeckhausen :

Lets look at what the DOT ratings mean. The table below shows the MINIMUM wet and dry boiling points for DOT 2, 3, 4, and 5 brake fluid in degrees fahrenheit.

DOT 2DOT 3DOT 4 DOT 5Dry Boiling point374401446500Wet boiling point284311356

The DOT 2 spec is for drum brakes and is obsolete. If you have any DOT 2 in your garage, throw it away! DOT 5 is for silicone brake fluid. Silicone brake fluid (DOT 5) should be avoided because it is not compatible with regular brake fluid, it is hard to pour without introducing bubbles and thus results in soft pedal feel, and moisture still gets into your system and will pool in low areas like your calipers and encourage rapid corrosion. STAY AWAY!

That leaves DOT 3 and DOT 4 fluids. These fluids are compatible with each other and may be interchanged or mixed with no ill effects.

Let's look at some popular brake fluids and their boiling points:

FluidDRYWETCastrol LMA DOT 3/4446311Ford Heavy Duty DOT 3 550290ATE Super Blue Racing536392ATE TYP 200536392Motul Racing 600585421Castrol SRF590518Performance Friction550284

Castrol LMA is very good at rejecting moisture and may be kept in your brake system for a couple years. The LMA stands for "Low Moisture Activity". This is the minimum quality stuff that I would use in my Impala. It comes in plastic containers which do not have a long shelf life. Don't buy lots of this stuff at a time because moisture can make its way through the plastic containers.

Ford Heavy Duty DOT 3 is VERY inexpensive and is popular among racers because of its excellent dry boiling point. It absorbs moisture quickly, but the racers don't care since they change their fluid frequently. Comes in metal cans so it may be stored. I would not use this in my Impala for the street.

ATE Super Blue Racing and ATE TYP 200 are the same brake fluid in two different colors (blue and amber, respectively). BMW recommends this brake fluid for their street cars because it, like Castrol LMA, absorbs moisture very slowly. The advantage over LMA is that ATE has a much better wet boiling point. You can put this stuff in your car and forget about it for a long time. An excellent choice for a weekend track car which also sees regular street duty. Comes in metal cans. This is what I use in all my street cars.

Motul Racing 600 is a very exotic and expensive synthetic fluid with high wet and dry boiling points. I use this exclusively in my race cars. Too expensive for the street and requires frequent changing due to its hygroscopic nature. Sold in plastic bottles. It is not suitable for the street because it absorbs moisture quickly.

Castrol SRF is a hyper-exotic and hyper-expensive brake fluid that is generally used by wealthy Porsche owners at track events. I've seen prices of $78 per liter for this stuff. Sold in metal cans. I can't afford this stuff!

Performance Friction High Performance DOT 3 has a good dry boiling point but a crummy wet boiling point. It comes in metal cans which is good for shelf life and sells for $7.87 per 16 ounce container. If you are even considering this fluid, I would go with the cheaper Ford Heavy Duty DOT 3. In either case, change this fluid frequently due to the poor wet boiling point.

Thanks to Leigh Smith for the following information on the impact of moisture content in brake fluid :

http://www.shotimes.com/pics/BrkFluid.jpgThe amount of moisture in brake fluid definitely affects its performance. The big problem is it is absorbs moisture quickly. Over a relatively short period of time brake fluid will absorb moisture from the air. SAE field tests have shown that the average one year old car has 2% moisture in the fluid. A random test of vehicles in the U.S. showed an average water content of 2.6% for vehicles with an average age of 8 years. And 25% of these vehicles had water content greater than 4%.

As water content in brake fluid increases over time, the boiling point decreases. Fluid with a reduced boiling point (or high water content) can create vapor by boiling in the caliper, or wheel cylinder. The result is sudden brake failure. And water in the brake fluid can contribute to corrosion of parts such as steel pistons and ABS modulators.

The end result is even though DOT 3 fluid is "rated" at greater than 401oF, in the typical 3 to 4 year old car with 3 to 4% moisture content, it could boil under 300oF. And if it has got more than 4% moisture, you may as well be running straight water!

Moral: Flush your brake fluid every year or so. But only if you would like it to work well scarcely an inch away from those toasty 500oF rotors on your SHO during a couple of hard stops! Or would you rather have a squishy pedal? Technical data courtesy of Leica Refractometers. www.leica-ead.com.

cheers

Ron

[Roy]

...

Motul Racing 600 is a very exotic and expensive synthetic fluid with high wet and dry boiling points. I use this exclusively in my race cars. Too expensive for the street and requires frequent changing due to its hygroscopic nature. Sold in plastic bottles. It is not suitable for the street because it absorbs moisture quickly. ...  

Thats what i have read about all good performaing fluids. The Motul is fine off the shelf because of the use of Nitrogen when sealing the container, but once in use the life of the fluid is compromised when compared to the cheaper low grade ethylene glycol brake fluids:(

The Castrol SRF could be the exception, at the asking price it could very well be. But at $30 / bottle for the Motul its cheap insurance to flush the whole bottle thru to make sure a day at the track isnt ruined by brake fluid related woes....well thats my 2 bux fitty anyway:(

[Ronin 09]

OK, so bottom line - lump the 30 bucks and do a flush? I do have a bottle that was used at the last brake fluid flush - ie. June (ish)