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2016 Limited 2.5
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Discussion Starter #1
I haven't changed the brake fluid at the recommended 30,000 mile interval, only because I don't ever recall having to change brake fluid in any other vehicle I've owned or own. That notwithstanding, I'm curious if anyone uses brake fluid testers (strips, or battery powered sensors) to check for water or corrosion level. I see both types for sale on Amazon with decent reviews. Thanks, and Happy New Year!
 

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2016 Outback Limited Titanium
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383 Posts
I haven't changed the brake fluid at the recommended 30,000 mile interval, only because I don't ever recall having to change brake fluid in any other vehicle I've owned or own. That notwithstanding, I'm curious if anyone uses brake fluid testers (strips, or battery powered sensors) to check for water or corrosion level. I see both types for sale on Amazon with decent reviews. Thanks, and Happy New Year!
Happy New Year. I used to use the strips in the past. But now just prefer to follow the manufacturers recommendations for maintenance items including flushing the brake fluid. Brake fluid is hydroscopic (absorbs moisture) and your braking system is very important to maintain. All vital fluids in the car will breakdown over time and should be replaced if you intend to keep the car for any long period of time. To me, car maintenance is a cost that needs t be factored in with the purchase price. As bad an investment as buying a car is, you have to consider the cost of maintenance as part of that bad investment. By keeping a car maintained properly, you minimize the pain and suffering of breakdowns later on and save money in terms of emergence repairs, roadside service and time lost. You can stretch out the change intervals of vital fluids but within reason.


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2015 Outback 2.5i Limited, Ice Silver/Black
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Never used the strips, but got an electronic tester from Amazon for Christmas. Tested my 5 year old OB's fluid and my 10 year old (to me) RX-7's fluid. Both tested green... Hmm. Maybe I got a dud. So I tested its accuracy by putting 1 tablespoon of fresh DOT 3 brake fluid (which tested green) and 3 drops of water in a pill bottle and shook it up. Those proportions should be ~1.3% water content. The <2% LED came on, so it seems to be reading correctly. Perhaps much of the brake fluid change rhetoric is just that. At any rate, I think my Subaru's brake flush schedule of 30 mos/30K is pretty ridiculous, considering they even describe the system as "sealed" in their FSM. But do or do not, IDGAF. Wait... I think my Yoda is cross-linked on my Dua Lipa...
 

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2016 Limited 2.5
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Discussion Starter #4
Never used the strips, but got an electronic tester from Amazon for Christmas. Tested my 5 year old OB's fluid and my 10 year old (to me) RX-7's fluid. Both tested green... Hmm. Maybe I got a dud. So I tested its accuracy by putting 1 tablespoon of fresh DOT 3 brake fluid (which tested green) and 3 drops of water in a pill bottle and shook it up. Those proportions should be ~1.3% water content. The <2% LED came on, so it seems to be reading correctly. Perhaps much of the brake fluid change rhetoric is just that. At any rate, I think my Subaru's brake flush schedule of 30 mos/30K is pretty ridiculous, considering they even describe the system as "sealed" in their FSM. But do or do not, IDGAF. Wait... I think my Yoda is cross-linked on my Dua Lipa...
Which tester did you receive from Amazon? I have a couple different ones on my wish list and trying to decide on one.
 

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2016 Outback Premium 2.5 CVT w/EyeSight+SRVD
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So I tested its accuracy by putting 1 tablespoon of fresh DOT 3 brake fluid (which tested green) and 3 drops of water in a pill bottle and shook it up. Those proportions should be ~1.3% water content. The <2% LED came on, so it seems to be reading correctly.
Excellent! There's no substitute for your own data.

Perhaps much of the brake fluid change rhetoric is just that. At any rate, I think my Subaru's brake flush schedule of 30 mos/30K is pretty ridiculous ...
Water absorption by brake fluid is highly dependent on long-term ambient humidity, and it's far more related to time than to mileage.

Apparently there is a fine mesh filter at the inlet side of the VDC/ABS hydraulic control unit that is particularly sensitive to brake fluid contamination by water. I think there was a TSB issued several years ago when water-contaminated brake fluid was introduced into a number of brand new Legacys and Outbacks at the factory.
 

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Which tester did you receive from Amazon? I have a couple different ones on my wish list and trying to decide on one.
ITEQ, but it does appear many are the same. Looked for the best/most reviews, but grain of salt there, too...
 

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Water absorption by brake fluid is highly dependent on long-term ambient humidity, and it's far more related to time than to mileage.
Also depends on the type of brake fluid. Most are glycol based and hygroscopic, except DOT 5, which is silicone based and not hygroscopic.
 

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Also depends on the type of brake fluid. Most are glycol based and hygroscopic, except DOT 5, which is silicone based and not hygroscopic.
So why haven't manufacturers switched to silicone fluid? Cost would be of minor consequence in a $30-40k car.
 

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So why haven't manufacturers switched to silicone fluid? Cost would be of minor consequence in a $30-40k car.
While DOT 5 is not hygroscopic and has a very high boiling point, good things, it can aerate in ABS systems causing a spongy brake pedal, a bad thing.
 

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Brake fluid is so cheap, there's no reason not to change it (other than being lazy).

In the Wrangler world, if you neglect it, the next time you swap pads it's almost a guarantee that shortly after you'll have a sticking piston/caliper.

As mentioned above, it is hygroscopic and absorbs moisture.

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I am more concerned about particulate contamination than water absorption. I have seen sediment in the bottom of master cyl reservoirs and suspended in fluid coming out of bleeder valves. The particulates are more of a concern with modern brake systems that have electromechanical solenoids such as in ABS controllers and brake assist systems.
The fluid testing doesn't measure particulate contamination.
Get a pressure bleeder (or device of your preference) and just do the regular maintenance.
 

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2016 Limited 2.5
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Discussion Starter #14
So I purchased these from Amazon Phoenix Systems Double ended strips. They test brake fluid on one side and coolant on the other.
Brake fluid was fine, but I wasn't able to test the coolant because the level was too low. I guess I should add some Subaru Super Coolant to the fill level. Probably good I checked, as I don't ever remember checking in the last 4 years.
 

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2012 Outback Ltd 3.6r
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Lets put it into a dollars and cents scenario. A can of brake fluid is fairly cheap, and the bleed, while a pain, not terribly difficult to do. The cost of a master cylinder, ABS pump, or even a wheel caliper that leaks or seizes can be an expensive repair. It's cheap insurance to ensure the fluid is clean, doesn't clog anything, keeps the seals stable, and help prevent corrosion in the system. - Fluid flush for the win in my book.

Just an FYI, at around 64k I replaced the pads and rotors on all four wheels, and flushed performed a full bleed/flush of the fluid, and she brakes like new again. (I was down close to the wear sensors on the fronts, and wasn't going to replace the pads and not bleed the system.....dealer bled them at 30k as part of the CPO maintenance).

Just my $0.02 on the topic.
 
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