I don't know how to test...and am fine following mfr recs on this service intervals.

 

This will open as much a can o' worms as "what's the best oil". I do it now, but I haven't done it on other car's I've owned. I have installed Speed Bleeders in my '15 to make it a one man job.

 

had the dealer do it at 30k because thats what they "wanted" and they recommended it. i also had it done around 96k when the dealer did the rotors and the pads.... flush and replaced.

 

I will not inquire about the need for transmission fluid change 🤞

 

I bleed/flush my brake fluid annually on all my cars. A couple bubbles come out each time and the fluid is slightly darker than the new fluid going in. It also helps keep the inside of the brake fluid reservoir clean.

I have a Motiv pressure bleeder which makes it a simple and quick, one man job. Set up the bleeder and then go around to each wheel and crank open the bleeder one at a time. This helps keep the calipers from getting rusty and clogged inside and ensures the bleeders never seize.

 

Annually is overkill for most driving, but it's your $. Brake fluid is hygroscopic and should be changed as recommended by OEM; typically every 3 years. Failure to do so increases the risk of moisture boiling in the fluid upon severe braking, causing reduced braking efficiency, thus perhaps an accident.

 

If you are comfortable with the test results (e.g., no major moisture issues) then no need to change. I just do our cars every 3-4 years. However, I do have friends who say "what is that?" and only do oil changes, and they are fine Plus I highly doubt your brake suddenly stops working because of "bad"fluid.

 

Plus I highly doubt your brake suddenly stops working because of "bad"fluid.

I'd call that going by faith. I'm going by what I learned as a mechanic, not faith, doubt or anything else.

 

It should be changed on some schedule.
One of the shortcomings of using test strips on the brake fluid is you are really only testing the fluid in the reservoir. The brake fluid is not circulated through the system like coolant or engine oil would be.
If you sample the fluid at the calipers too, that gives a better picture of fluid health.

 

It should be changed on some schedule.
One of the shortcomings of using test strips on the brake fluid is you are really only testing the fluid in the reservoir. The brake fluid is not circulated through the system like coolant or engine oil would be.
If you sample the fluid at the calipers too, that gives a better picture of fluid health.

That is a very good point.

 

Do I do it? No.
Do I have it done? Oh hell yes. Brake fluid is hygrosopic, so changing it helps prolong the system and keep it from rusting from the inside out.

 

The manual says to change it every 30k miles, so I take it to the shop and have them do it. Its pretty inexpensive in the scheme of things, and I'm not looking to save a few bucks when it comes to brakes.

 

it s cheap insurance, fluid is cheap. I do mine every two years or so . I do it on a tire rotation or brake job so I already have wheels off so no extra work.

 

Follow OEM recommended maintenance to insure all warrranty conditions are met in my opinion....Once past warranty window.......individual decision on how often to do it.

 

Honestly Subaru's intervals for changing it are very short. Inspecting/testing it however, that should be done regularly. Most modern brake fluid will easily last 5 years, but it depends on your use. Manufacturers are all over the map on how often to do it, with some never recommending it.

Have it tested. If the moisture content is at 3%, change it. If it is at 2% and low in the reservoir, also change it. Otherwise you are generally A-OK to leave it.

And yes I am a big proponent of changing transmission fluid every 60,000 miles.

 

I change mine in all my vehicles every 3 years regardless of mileage. Brake fluid loves to attract moisture.

Get some speed bleeders to make the job quicker and easy to do.

 

Have never heard a legit reason not to change it on recommended interval. And lots of reasons to do so as has already been stated above.

 

My current Subaru is 22 years old. I bought her about a month ago and changed all the fluids like I do with all of my older cars from time to time. Nothing last forever and it gives me an excuse to get out of my wife’s hair.

 

Contaminated and bad are two different things. You never want contamination. That will swell any and all rubber in the system.

As the others have mentioned, brake fluid is hygroscopic. It sucks up water. Pour some on the back of your hand. You'll feel it get hot as it sucks the water out of you skin cells. If you fill a shot glass with brake fluid to the rim, it will continue to overflow as it sucks water from the air. As you get water in the system, it settles in the low spots being the calipers. Most caliper bores are chrome lined, most pistons are not. Water gets on the piston, you get rust. Rust ceases stuff up. Water can boil and you get air in the system.

Test strips are going to test for acidity and the presence of copper. Both of which you will see little in the reservoir. Copper from the lines will settle in the calipers, and acerbate the rust build up. Acidity will be the lowest in the resivor as the cap is vented to atmosphere, an this is where the moisture starts.

Follow the maintenance manual for flush. If in doubt, every fluid in the car should have been flushed somewhere between 60-75k miles.

 

I don't think there's any water solubility limit for DOT 3 or 4 (glycol ether-based) brake fluids, so it's not possible for water to separate out of them and collect in low spots, it should diffuse relatively evenly throughout the entire system (that doesn't mean they don't become more corrosive as they absorb water however). That's why you can use a conductivity meter at the reservoir to get a reasonable estimate of the water content. I had my fluid changed at around 5 years of age and it was still well under the maximum allowable water content. Those meters do tend to be cheaply built however, so their accuracy sometimes comes into question (since I work in a lab I was able to confirm that my meter was correctly calibrated).

However, phase-separation of water is a problem with DOT 5 (silicone-based) fluids, as they have basically zero miscibility with water (very low to zero solubility).

 

... phase-separation of water is a problem with DOT 5 (silicone-based) fluids, as they have basically zero miscibility with water (very low to zero solubility).

DOT 5 fluid is also totally incompatible with DOT 3 or 4 brake fluids. DO NOT MIX THEM.

For completeness, most aircraft brake fluids are petroleum based and thus are incompatible with any DOT-spec fluid. DO NOT MIX THEM.

(To confuse things further, there is a DOT 5A fluid that is an acceptable replacement for DOT 3/4, but it's not recommended.)

 

Don't put DOT5 in a DOT3/4 system.

 

Did brake flush last weekend. Here is fluid before and after. Took me 45 min and 1L of new fluid.

Sent from my Pixel 6 using Tapatalk

 

Are you sure those aren't two types of beer?🍺

 

I have a 2019 Subaru outback. The maintenance manual shows "brake fluid/clutch fluid (MT only)" replacement schedule. Here MT = manual transmission. For the CVT auto transmission, I guess no need to change the brake fluid. Let me know your thought.

 

You are reading it wrong.

You have brake fluid, it should be flushed every 5 years. For those Outbacks with manual tranny's they also should flush the clutch fluid at the same time.

That's what that means.

 

Thanks for the explanations!

 

Just an FYI. (Ford) Motorcraft dot 3 and dot 4 has considerably higher boiling points than others. So if you are doing track stuff. May wish to try motorcraft.

 

where did you find that info.. the difference in boiling point is between DOT3 and 4.. have not seen anything showing motorcraft has higher BP than normal DOT3 or 4.. DOT4 has higher BP so better for brake system in the south where the humidity is higher year around.. most likely make no difference in AZ other than the air and road temps in summer are higher a dot 4 would be better for that.. overall dot4 is the best for non race brakes.

 

Just bleed my lines last week. 3 years/32.7k miles. Used (2) 12 oz bottles of the Subaru branded stuff so this is probably lightened by 1/4 of new fluid. Maybe someone in Arizona could go 5 years, but here in NYC that's what 3 years looks like. I already picked up some Bosch LV fluid for the newer cars. That should last an extra year compared to Dot 3/4.

 

a lot darker than mine was - I did mine at 4.5 years or so, a little less mileage, and I could hardly tell the color difference of the old vs the new. The rears were a touch darker than the fronts. Barely.