Is it necessary to replace brake fluid on a car every 3 years?

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bluegill
Posts: 210
Joined: Thu Oct 04, 2018 11:15 am

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by bluegill »

NO.
Brake fluid will not absorb moisture if you put the cap on the reservoir.
There is DOT 3 and DOT 4 fluid. Type 4 has high temperature tolerance. If you have moisture in a brake line, close to very hot brakes, the DOT 4 will not become inoperatable, while the DOT 3 will fail sooner.
It might be a good idea to change fluid if you are a car racer; race cars brakes get very hot.
Last edited by bluegill on Sun Nov 28, 2021 8:28 am, edited 1 time in total.
twh
Posts: 142
Joined: Sat Feb 08, 2020 3:15 pm

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by twh »

bluegill wrote: Wed Nov 24, 2021 2:15 pm NO.
Brake fluid will not absorb moisture if you put the cap on the reservoir.
There is type 2 and type 3 fluid. Type 3 has high temperature tolerance.
It might be a good idea to change fluid if you are a car racer; race cars brakes get very hot.
This is incorrect. Brake fluid will absorb moisture regardless of the cap. Many caps are even vented, but regardless, the fluid will absorb moisture.

I have no idea what you are talking about type 2 and type 3. The prevailing brake fluid standards that covers 99% of cars are DOT 3 and DOT 4.
Soon2BXProgrammer
Posts: 2815
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Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by Soon2BXProgrammer »

twh wrote: Wed Nov 24, 2021 1:37 pm
valleyrock wrote: Wed Nov 24, 2021 1:20 pm
Soon2BXProgrammer wrote: Mon Nov 22, 2021 9:42 am
valleyrock wrote: Mon Nov 22, 2021 8:14 am One approach I've considered for transmission fluid is lab testing.
Maybe its just been my experience with transmissions, but I find value in doing transmission fluid drain and fills. Maybe its because I had an early generation CVT and it was especially important for those. (if you didn't do it, it cause premature failure)
Good point. Lately I've been using my MightyVac to pull out around 2 quarts of transmission fluid every year, then I replace with new at about the same temperature so as to keep the volumes consistent. That obviously does not get out all the fluid, but it is probably equivalent to a full drain and fill every 5 years or so. And that does not change the filter, of course, which is accessible only by dropping the transmission pan. (Of course, pulling out what one can with a MightyVac does help when dropping the pan... less messy that way).

To get back on-topic, MightyVacs do have a brake fluid attachment but I haven't tried it, and now I'm tempted to get a Motive brake bleeder as mentioned above.

The price of a tool like this is paid for the first time it's used, but, indeed, a person should really know what they're doing when messing with brakes.
At least for most transmissions, even dropping the transmission oil pan does not drain all the transmission fluid. There is a lot (quarts) held up in various parts of the transition. My point is that partial exchange isn't a bad idea.
Maybe its just me and the horror stories i've heard, but i'm hesitant to do the true ATF exchange service... i just drain and fill it which only does partial.
Earned 34 (and counting) credit hours of financial planning related education from a regionally accredited university, but I am not your advisor.
illumination
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Joined: Tue Apr 02, 2019 6:13 pm

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by illumination »

I'm in the camp that even though it may be ideal to flush it that often, I don't do it. It's a wallet flush for the dealerships. I would make a significant wager a lot of the times when a dealership charges for a brake flush, they don't actually flush the brakes. I don't buy for a minute it needs to be changed that often anyway and I think someone is more likely to screw something up than whatever benefit you get from fresh brake fluid. I do think it does eventually need to be pulled out, but I would most systems could comfortably go past 7+ years without any issue. It's a closed system and the fluid's primary purpose is hydraulic pressure.
Kagord
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Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by Kagord »

twh wrote: Wed Nov 24, 2021 2:30 pm
bluegill wrote: Wed Nov 24, 2021 2:15 pm NO.
Brake fluid will not absorb moisture if you put the cap on the reservoir.
There is type 2 and type 3 fluid. Type 3 has high temperature tolerance.
It might be a good idea to change fluid if you are a car racer; race cars brakes get very hot.
This is incorrect. Brake fluid will absorb moisture regardless of the cap. Many caps are even vented, but regardless, the fluid will absorb moisture.

I have no idea what you are talking about type 2 and type 3. The prevailing brake fluid standards that covers 99% of cars are DOT 3 and DOT 4.
Well, technically, brake fluid won't absorb moisture is there is none to be had. For instance, in outer space.

Image
lazydavid
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Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by lazydavid »

Soon2BXProgrammer wrote: Wed Nov 24, 2021 2:41 pm Maybe its just me and the horror stories i've heard, but i'm hesitant to do the true ATF exchange service... i just drain and fill it which only does partial.
Correct, you do not want to do a "powerflush" on most automatic transmissions. Last time I did it on my wife's previous car, I just did 4 or 5 drain and refills in a row with a couple of minutes of driving in between each to circulate the fluid. I only worried about getting the fill exactly right on the last fill. That should have gotten me to about 97-98% new fluid, which is good enough. A case of synthetic Toyota WS-compatible fluid cost me just over $100.

On my car the process to get the fill level exactly right is super fiddly and the ZF trans fluid is more expensive than unicorn blood (retail $37/quart!), so it cost about the same to take it to an independent mechanic and get it done right, including replacing the pan, filter, all the bolts and all the seals.
neilpilot
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Location: Memphis area

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by neilpilot »

illumination wrote: Wed Nov 24, 2021 2:53 pm I'm in the camp that even though it may be ideal to flush it that often, I don't do it. It's a wallet flush for the dealerships. I would make a significant wager a lot of the times when a dealership charges for a brake flush, they don't actually flush the brakes. I don't buy for a minute it needs to be changed that often anyway and I think someone is more likely to screw something up than whatever benefit you get from fresh brake fluid. I do think it does eventually need to be pulled out, but I would most systems could comfortably go past 7+ years without any issue. It's a closed system and the fluid's primary purpose is hydraulic pressure.
Aren't all dealer service items "a wallet flush"? Why would you have the dealer do any maintenance to your car, other than warranty repairs and recalls?
twh
Posts: 142
Joined: Sat Feb 08, 2020 3:15 pm

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by twh »

lazydavid wrote: Wed Nov 24, 2021 3:09 pm
Soon2BXProgrammer wrote: Wed Nov 24, 2021 2:41 pm Maybe its just me and the horror stories i've heard, but i'm hesitant to do the true ATF exchange service... i just drain and fill it which only does partial.
Correct, you do not want to do a "powerflush" on most automatic transmissions. Last time I did it on my wife's previous car, I just did 4 or 5 drain and refills in a row with a couple of minutes of driving in between each to circulate the fluid. I only worried about getting the fill exactly right on the last fill. That should have gotten me to about 97-98% new fluid, which is good enough. A case of synthetic Toyota WS-compatible fluid cost me just over $100.

On my car the process to get the fill level exactly right is super fiddly and the ZF trans fluid is more expensive than unicorn blood (retail $37/quart!), so it cost about the same to take it to an independent mechanic and get it done right, including replacing the pan, filter, all the bolts and all the seals.
+1...I'm not advocating power flushing. Drain out some and refill the same amount.
twh
Posts: 142
Joined: Sat Feb 08, 2020 3:15 pm

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by twh »

illumination wrote: Wed Nov 24, 2021 2:53 pm a lot of the times when a dealership charges for a brake flush, they don't actually flush the brakes
That may be the case, but that's a different problem :) I flush my BMW every 2 years and other cars in the family every 3 or 4 years depending on when I package it with another messy job or just feel like it.
twh
Posts: 142
Joined: Sat Feb 08, 2020 3:15 pm

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by twh »

Kagord wrote: Wed Nov 24, 2021 2:57 pm
twh wrote: Wed Nov 24, 2021 2:30 pm
bluegill wrote: Wed Nov 24, 2021 2:15 pm NO.
Brake fluid will not absorb moisture if you put the cap on the reservoir.
There is type 2 and type 3 fluid. Type 3 has high temperature tolerance.
It might be a good idea to change fluid if you are a car racer; race cars brakes get very hot.
This is incorrect. Brake fluid will absorb moisture regardless of the cap. Many caps are even vented, but regardless, the fluid will absorb moisture.

I have no idea what you are talking about type 2 and type 3. The prevailing brake fluid standards that covers 99% of cars are DOT 3 and DOT 4.
Well, technically, brake fluid won't absorb moisture is there is none to be had. For instance, in outer space.

Image
Exactly...the ancient aliens absorbed all the moisture from the solar system when they left the caps off the spaceship brakes :)
eddot98
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Location: The Berkshires

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by eddot98 »

Although I understand the theory about changing brake fluid because it can absorb water, which could cause lots of problems, I just haven’t done it in the past 20 or so years. During that time we had 6 Camry’s that all had over 140,000 miles when they were traded in and none of them ever had their brake fluid changed. None had any brake issues while we owned them.
Also, 5 of them had automatic transmissions and we never changed the fluid in any of them and we never had transmission problems. The 6th had a standard transmission.
valleyrock
Posts: 296
Joined: Sun Aug 12, 2018 7:12 am

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by valleyrock »

twh wrote: Wed Nov 24, 2021 1:37 pm
valleyrock wrote: Wed Nov 24, 2021 1:20 pm
Soon2BXProgrammer wrote: Mon Nov 22, 2021 9:42 am
valleyrock wrote: Mon Nov 22, 2021 8:14 am One approach I've considered for transmission fluid is lab testing.
Maybe its just been my experience with transmissions, but I find value in doing transmission fluid drain and fills. Maybe its because I had an early generation CVT and it was especially important for those. (if you didn't do it, it cause premature failure)
Good point. Lately I've been using my MightyVac to pull out around 2 quarts of transmission fluid every year, then I replace with new at about the same temperature so as to keep the volumes consistent. That obviously does not get out all the fluid, but it is probably equivalent to a full drain and fill every 5 years or so. And that does not change the filter, of course, which is accessible only by dropping the transmission pan. (Of course, pulling out what one can with a MightyVac does help when dropping the pan... less messy that way).

To get back on-topic, MightyVacs do have a brake fluid attachment but I haven't tried it, and now I'm tempted to get a Motive brake bleeder as mentioned above.

The price of a tool like this is paid for the first time it's used, but, indeed, a person should really know what they're doing when messing with brakes.
At least for most transmissions, even dropping the transmission oil pan does not drain all the transmission fluid. There is a lot (quarts) held up in various parts of the transition. My point is that partial exchange isn't a bad idea.
Oh, absolutely. (There's some software out there to determine how many partial exchanges it takes to get close to a full exchange.) The idea is to renew (even if partially) the additives in the fluid, so it retains its lubrication properties, keeps seals conditioned, etc. Did I ever mention my girlfriend from years ago who studied lubrication engineering in graduate school? She was very educational!

My opinion is that any of these procedures is far preferable to letting the dealer do a transmission fluid flush. That doesn't change the filter, of course, just as extracting with a MightyVac doesn't. All my car manuals say that the procedure to use is to drop the pan, change the filter, replace the pan, and add new fluid. There's no mention of performing a fluid flush, and for that reason alone, it's a bad idea to let a dealer do one. Actually there's not much reason to let a dealer anywhere near a car unless it's to address a recall.
Independent George
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Location: Chicago, IL, USA

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by Independent George »

You can always order a test kit and send it to a lab for analysis. Once you have your first positive result, you'll have a better estimate on when the next fluid change will be needed based on mileage rather than a calendar. I've never done it for brake fluid, but oil analysis is only $30-$40.
neilpilot
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Location: Memphis area

Re: Is it necessary to replace brake fluid on a car every 3 years?

Post by neilpilot »

Independent George wrote: Fri Nov 26, 2021 2:26 pm You can always order a test kit and send it to a lab for analysis. Once you have your first positive result, you'll have a better estimate on when the next fluid change will be needed based on mileage rather than a calendar. I've never done it for brake fluid, but oil analysis is only $30-$40.
Almost as much a syn oil & filter. Easier to just change oil. Analysis is useful to track condition of motor if regular samples are run, but a waste if it's done to decide on an oil change.
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