[Shovelman]

Oil changes, of course, oil is exposed to lots of outside contamination. But coolant, brake fluid, transmission and axle fluid are in sealed environments. My DD garaged, no mountains, no dirt roads, moderate driving, never tracked, normally 30 miles of highway a few times a week, Michigan weather. These are pretty good conditions. I'm thinking these fluids can last a long time.

[aerobod]

Brake fluid certainly deteriorates even if the vehicle isn't used, as the system has a breather in it to allow for volume changes as the brake pads wear. With it being highly hygroscopic, the climate in which the car is stored will determine the moisture absorption rate, but it is only a matter of time before it reaches the max moisture content rate of about 3% before standard DOT 3/4/5.1 fluid starts to corrode the brake system due to being unable to absorb any more moisture from the air.

[Ajowhan]

Originally Posted by aerobod

Brake fluid certainly deteriorates even if the vehicle isn't used, as the system has a breather in it to allow for volume changes as the brake pads wear. With it being highly hygroscopic, the climate in which the car is stored will determine the moisture absorption rate, but it is only a matter of time before it reaches the max moisture content rate of about 3% before standard DOT 3/4/5.1 fluid starts to corrode the brake system due to being unable to absorb any more moisture from the air.

And coming fresh from the factory, it is generally accepted 3 years is a good length of time to change your brake fluid and every 2 years thereafter.

[Sportstick]

Originally Posted by Ajowhan

And coming fresh from the factory, it is generally accepted 3 years is a good length of time to change your brake fluid and every 2 years thereafter.

I am not following this logic and who is doing the accepting. The fluid doesn't know if it was put in at the factory or at a dealer...fresh is fresh and being susceptible to absorbing humidity is a constant. Why delay the first refill, especially in the OP's area surrounded by the Great Lakes? If you follow Mike Miller's Lifetime Maintenance Schedule for those planning to keep their cars long-term, brake fluid change is annual, which was also BMW's recommended maintenance before they started paying for it, as Mike notes in his document. Coolant is every two years. More to read here:

https://www.dslreports.com/r0/downlo...e%20v03.13.pdf

[Ajowhan]

Originally Posted by Sportstick

I am not following this logic and who is doing the accepting. The fluid doesn't know if it was put in at the factory or at a dealer...fresh is fresh and being susceptible to absorbing humidity is a constant. Why delay the first refill, especially in the OP's area surrounded by the Great Lakes? If you follow Mike Miller's Lifetime Maintenance Schedule for those planning to keep their cars long-term, brake fluid change is annual, which was also BMW's recommended maintenance before they started paying for it, as Mike notes in his document. Coolant is every two years. More to read here:

https://www.dslreports.com/r0/downlo...e%20v03.13.pdf

You are right, thanks for correcting me. I have somehow mixed what Im reading somewhere else with Mike Miller's schedule.

In the end, if you really wanna know for sure if its time for you to change, test the moisture content of your brake fluid.

[Shovelman]

Fresh from the factory is definitely better than a refill. The factory has a machine that pulls a vacuum, fills and seals with no chance of contamination or contact with air, and there are quality checks at critical points.

Not sure on BMW but on most cars the breather air is separated from the fluid by a rubber diaphragm.

Coolant is another matter. It does breath outside air but it is not hygroscopic.

[aerobod]

Originally Posted by Shovelman

Not sure on BMW but on most cars the breather air is separated from the fluid by a rubber diaphragm.

A rubber diaphragm isn't enough to equalise the pressure in the master cylinder to allow for brake wear between the min and max fluid mark in the master cylinder with the caliper piston volume on the 2-series, it would require a fairly large bellows system that could expand to fill the full volume. I don't know of any European car that uses a bellows system to account for volume change, they all use a seal on the cap with a very small vent hole that is baffled to prevent fluid spill, to equalise the pressure.

[Lucky13]

Originally Posted by Ajowhan

And coming fresh from the factory, it is generally accepted 3 years is a good length of time to change your brake fluid and every 2 years thereafter.

Oh I’m 100% certain that that is because free service runs out at 3 years. I’m still looking for someone to explain why when BMW puts it in it lasts 3 years but when we pay for it it only is good for two. Now all those on here say you have to not listen to what BMW says about how long all the fluids last but everyone accepts this bs. It either lasts 2 years or it lasts 3 years but not both.

[Ajowhan]

Originally Posted by Lucky13

Oh I’m 100% certain that that is because free service runs out at 3 years. I’m still looking for someone to explain why when BMW puts it in it lasts 3 years but when we pay for it it only is good for two. Now all those on here say you have to not listen to what BMW says about how long all the fluids last but everyone accepts this bs. It either lasts 2 years or it lasts 3 years but not both.

To my understanding, it is because when they come from the factory, they were vacuum filled. There is no air with moisture in the system to be absorbed by the fluid. When we flush and refill the fluid, the fluid come into contact with air with moisture early on and thus needed shorter interval.

Please correct me if I am wrong.

[Lucky13]

Standard practice by anyone changing brake fluid is to bleed the brakes (pump all the air out) so that theory is bs if BMW told you that.

[aerobod]

Originally Posted by Lucky13

Standard practice by anyone changing brake fluid is to bleed the brakes (pump all the air out) so that theory is bs if BMW told you that.

The free space in the master cylinder reservoir still contains air after a brake bleed. Fluid in the brake system is always mixing from end to end and coming into contact with the air in the master cylinder reservoir, as can be seen after a trackday when the contaminated/oxidised fluid near the caliper pistons makes its way back into the fluid reservoir over a short period of time and discolours it (unless you bleed off 50cc or so from each caliper immediately after the event).

After the initial factory brake fluid fill where the fluid is pure and uncontaminated, all subsequent bleeds will always have some level of old fluid in the system mixed with the new fluid, unless all components and lines are removed and completely cleaned. It seems reasonable if that is the case to have a shorter fluid change interval after bleeds subsequent to the initial fill.

[Sportstick]

Originally Posted by Ajowhan

To my understanding, it is because when they come from the factory, they were vacuum filled. There is no air with moisture in the system to be absorbed by the fluid. When we flush and refill the fluid, the fluid come into contact with air with moisture early on and thus needed shorter interval.

Please correct me if I am wrong.

Not disputing the quality of the factory fill, but the issue is not the moisture present at the start. The issue is the progressive deterioration of the fluid to absorbing moisture over time. You may well be correct that after-factory refills have a head-start on this deterioration, but the fluid will deteriorate in its environment at its natural rate regardless of how "dry" it was on day 1.

https://epicbleedsolutions.com/blogs...oiling%20point.

[dradernh]

Originally Posted by Ajowhan

Please correct me if I am wrong.

You can use a brake fluid tester like one of these to determine the moisture content of your system's fluid: https://www.ecstuning.com/Search/Sit..._fluid_tester/. Note that our cars use DOT 4 brake fluid.

Note also that there is a non-hygroscopic brake fluid on the market: Castrol SRF. Bimmerworld offers a good description of the product's pros and cons here: https://www.bimmerworld.com/Castrol-...ake-Fluid.html. When I was still going to the track, I used SRF and had the brake fluid flushed before each track event and after the last event of the year. (Here, our season runs from April - November.)

[MarcoZandrini]

Originally Posted by Ajowhan

To my understanding, it is because when they come from the factory, they were vacuum filled. There is no air with moisture in the system to be absorbed by the fluid. When we flush and refill the fluid, the fluid come into contact with air with moisture early on and thus needed shorter interval.

Please correct me if I am wrong.

You are correct.

[aerobod]

All rubber brake lines (whether PTFE lined or not) have slight porosity to both air and water vapour molecules. It doesn’t matter how sealed or not the system is, there will be some absorption in any case, with the water vapour molecules actually being smaller than nitrogen and oxygen molecules, so more likely to pass through both the PTFE and EPDM molecular structure (as a common rubber used in flexible brake lines), especially in hot or humid environments.

Here is some info on material permeability and why silicone rubber in particular is a poor choice for flexible brake lines: https://www.versaperm.com/materials/...rmeability.php

[mleskovar]

How do you turn off the brake fluid warning light/message? I use a meter to measure the water in the fluid, not time.

[dmaxdmax]

You can reset through cluster somehow, I'm sure. If not, Bimmercode, or a scanner...

[GoldenWest]

Originally Posted by Sportstick

I am not following this logic and who is doing the accepting. The fluid doesn't know if it was put in at the factory or at a dealer...fresh is fresh and being susceptible to absorbing humidity is a constant. Why delay the first refill, especially in the OP's area surrounded by the Great Lakes? If you follow Mike Miller's Lifetime Maintenance Schedule for those planning to keep their cars long-term, brake fluid change is annual, which was also BMW's recommended maintenance before they started paying for it, as Mike notes in his document. Coolant is every two years. More to read here:

https://www.dslreports.com/r0/downlo...e%20v03.13.pdf

An older post I realize, but with brake fluid, I don’t go by timeframe or mileage; but by feel and performance.
Just flushed the brake fluid on my 2020 230i (w/track handling package), which had been done previously 1yr and 10K ago at the dealer under the included maintenance period.
I decided to flush the fluid because the pedal had lost a firm feel.
I used Ate SL6 with a Motive pressurized tank. 1 yr old fluid came out a medium dark yellow; like a slightly oxidized white wine. New fluid was much lighter and clearer The result was a much firmer pedal. “Proof is in the pudding!”

[XutvJet]

A $15 brake fluid tester goes a long way. It's been my experience that unless you're tracking the car, brake fluid changes can typically go 3-5 years before the water content gets to 3% or greater) and necessitating a replacement. I have NEVER experienced brake fade in any car on the street in my 35 years of driving and my cars have gotten 4-6 year brake fluid replacements.