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      08-29-2019, 08:58 AM   #1
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Brake Fluid - Frequency of Change?

For the past few years I've been changing out my brake fluid every spring, and I typically have no more than 4 track days per year (5 30-minute sessions each).

This year, I've only had 2 track days, and plan on having a third in the next month.

I've always used Super DOT 4 brake fluid (according to my service dept. - the highest grade brake fluid you can use without voiding your factory warranty - at least for brakes). I have stock (non-stainless steel) brake lines. I run Bridgestone RE-71R's and use Pagid RS-29's when on track (stock brake pads on street).

I've never had problems with brakes before - but out of an abundance of caution I thought I'd check in with everyone here and see if there are any "rules of thumb" for swapping out brake fluid more than once a year, depending upon the amount of track sessions each season (or any other parameters that might be relevant).
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      08-29-2019, 09:46 AM   #2
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There's a bunch of people on here that recommend brake fluid swap after each track day. It's complete overkill.

Your brakes operate on a simple hydraulic system and the fluid should only be changed if the moisture content increases or if it boils which you will notice in the pedal immediately. A brake fluid change is not a maintenance thing but whether you track or not, it will absorb moisture overtime which will drop the boiling point (wet boiling point).

That being said, BMW decided that they would put absolutely ZERO effort in brake cooling for the f8x so there's a good chance you'll get the temperatures high enough to boil your fluids. This of course depends on the track and which fluid you're running. I've boiled the stock fluid pretty quickly but there's a lot of guys on here that use it exclusively with zero issues. I'm pre-ABS on all corners and at placed like Watkins Glen and Limerock even Motul 600 may not last on a hot day.

If you do 4 track days a year, you'll be fine with 1 brake fluid change annually but if you boil it or get moisture in it (which you'll feel) you should change it. Fortunately brake fluid is cheap and easy to change.

The beauty of simple hydraulics is that you'll know immediately when it's not working as it used to.
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      08-29-2019, 11:31 AM   #3
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OP, your current method is fine, once or twice a year is fine unless you feel something out of the ordinary.


Quote:
Originally Posted by NYG View Post
There's a bunch of people on here that recommend brake fluid swap after each track day. It's complete overkill.

Your brakes operate on a simple hydraulic system and the fluid should only be changed if the moisture content increases or if it boils which you will notice in the pedal immediately. A brake fluid change is not a maintenance thing but whether you track or not, it will absorb moisture overtime which will drop the boiling point (wet boiling point).

That being said, BMW decided that they would put absolutely ZERO effort in brake cooling for the f8x so there's a good chance you'll get the temperatures high enough to boil your fluids. This of course depends on the track and which fluid you're running. I've boiled the stock fluid pretty quickly but there's a lot of guys on here that use it exclusively with zero issues. I'm pre-ABS on all corners and at placed like Watkins Glen and Limerock even Motul 600 may not last on a hot day.

If you do 4 track days a year, you'll be fine with 1 brake fluid change annually but if you boil it or get moisture in it (which you'll feel) you should change it. Fortunately brake fluid is cheap and easy to change.

The beauty of simple hydraulics is that you'll know immediately when it's not working as it used to.
Lord, I hope no one on here would suggest after every event!
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Last edited by OhioRiderAaron; 08-29-2019 at 01:40 PM..
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      08-29-2019, 12:12 PM   #4
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Quote:
Originally Posted by NYG View Post
There's a bunch of people on here that recommend brake fluid swap after each track day. It's complete overkill.

Your brakes operate on a simple hydraulic system and the fluid should only be changed if the moisture content increases or if it boils which you will notice in the pedal immediately. A brake fluid change is not a maintenance thing but whether you track or not, it will absorb moisture overtime which will drop the boiling point (wet boiling point).

That being said, BMW decided that they would put absolutely ZERO effort in brake cooling for the f8x so there's a good chance you'll get the temperatures high enough to boil your fluids. This of course depends on the track and which fluid you're running. I've boiled the stock fluid pretty quickly but there's a lot of guys on here that use it exclusively with zero issues. I'm pre-ABS on all corners and at placed like Watkins Glen and Limerock even Motul 600 may not last on a hot day.

If you do 4 track days a year, you'll be fine with 1 brake fluid change annually but if you boil it or get moisture in it (which you'll feel) you should change it. Fortunately brake fluid is cheap and easy to change.

The beauty of simple hydraulics is that you'll know immediately when it's not working as it used to.
+1
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      08-29-2019, 12:12 PM   #5
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Quote:
Originally Posted by OhioRiderAaron View Post
Lord, I hope no one on here would suggest after ever event!
I'm pretty sure someone posted that they change their oil and brake fluid every track day and differential fluid every 3 track days. I guess people love wasting their money.
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      08-29-2019, 02:00 PM   #6
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You can get a brake fluid tester on Amazon for around $10. This is like what they use at the tech inspection.

It measures the moisture in your fluid. When I was testing it i found some new, normal grade auto parts store fluid will already have some moisture immediately upon open.

Testing my Motul RBF600 showed zero moisture. So start with good fluid first, then measure as needed.
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      08-29-2019, 07:37 PM   #7
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Quote:
Originally Posted by Geez3 View Post
You can get a brake fluid tester on Amazon for around $10. This is like what they use at the tech inspection.

It measures the moisture in your fluid. When I was testing it i found some new, normal grade auto parts store fluid will already have some moisture immediately upon open.

Testing my Motul RBF600 showed zero moisture. So start with good fluid first, then measure as needed.
Great replies everyone - thanks!
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      09-01-2019, 10:25 PM   #8
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I use Castrol SRF in my Ferrari F430 and plan to do the same with my M4. My understanding is that it is considered the best brake fluid for track use.
I also plan to use Carbotech XP pads, 10 on rear 12 on front.
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      09-02-2019, 05:12 AM   #9
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It is a good habit to bleed off a small amount from each caliper after each track day, but there is no need to replace all the fluid. The fluid in the caliper will have seen the most extreme heat exposure. By bleeding it off you have a look at it, ie discolouration, and remove any small bubbles. This will also firm up the feel of the pedal.

If you are doing a lot of track days and you bleed a small amount after each event, you effectively are replacing all the fluid after around 8-10 events. If you only do a few a year, then a complete system bleed once a year is more than enough
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      09-02-2019, 02:48 PM   #10
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Quote:
Originally Posted by SCKOMS View Post
I use Castrol SRF in my Ferrari F430 and plan to do the same with my M4. My understanding is that it is considered the best brake fluid for track use.
I also plan to use Carbotech XP pads, 10 on rear 12 on front.
If I recall correctly, BMW does not advise using brake fluid with silicon in it. SRF is the best but be aware of this.
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      09-02-2019, 03:53 PM   #11
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Quote:
Originally Posted by NYG View Post
I'm pretty sure someone posted that they change their oil and brake fluid every track day and differential fluid every 3 track days. I guess people love wasting their money.
is it a waste of money though, if the car is a long term keeper?

Add up the cost of fuel, tow, entry fee, tires, hotel/camping and food. is another couple of quarts of oil and brake fluid really going to matter to your annual budget?

My $0.02 would be to change all the fluids every 5-10 hours, which is about what OP is doing with a 4x per year schedule
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      09-02-2019, 05:19 PM   #12
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Quote:
Originally Posted by nicknaz View Post
is it a waste of money though, if the car is a long term keeper?

Add up the cost of fuel, tow, entry fee, tires, hotel/camping and food. is another couple of quarts of oil and brake fluid really going to matter to your annual budget?

My $0.02 would be to change all the fluids every 5-10 hours, which is about what OP is doing with a 4x per year schedule
It is a ridiculous waste of money and it adds up. If you're already spending this much money on tracking, why contribute more than what is required. Your brake lines aren't connected to any other part of your car except your master cylinder and calipers. You're quite literally just flushing money down the toilet for the sake of "Well, I spend a lot as is, not going to hurt if I spend some more."

I can justify changing your tires after every event more than I can brake fluid.

If it makes you feel better to change it after every track day then by all means, go for it. Doesn't mean you're not wasting your money needlessly.
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      09-02-2019, 08:19 PM   #13
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Quote:
Originally Posted by NYG View Post
Quote:
Originally Posted by SCKOMS View Post
I use Castrol SRF in my Ferrari F430 and plan to do the same with my M4. My understanding is that it is considered the best brake fluid for track use.
I also plan to use Carbotech XP pads, 10 on rear 12 on front.
If I recall correctly, BMW does not advise using brake fluid with silicon in it. SRF is the best but be aware of this.
SRF is undoubtedly a better and more capable brake fluid than the Super DOT 4 that I use - but the Service Dept at my dealership said that would void the warranty for the brakes (the silocone based brake fluids can foam up from the ABS being triggered - which can cause brake system damage - which would alert the service tech to the use of silicone brake fluid - which would mean no warranty coverage).

I think more advanced drivers could justify the potential voiding of warranty coverage - but at my level (novice to intermediate) Super DOT 4 is more than sufficient...
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      09-05-2019, 06:35 PM   #14
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Run SRF, bleed once a year, be happy

SRF appears to be in short supply right now for whatever reason
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      09-05-2019, 06:36 PM   #15
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Quote:
Originally Posted by Powerslide View Post
SRF is undoubtedly a better and more capable brake fluid than the Super DOT 4 that I use - but the Service Dept at my dealership said that would void the warranty for the brakes (the silocone based brake fluids can foam up from the ABS being triggered - which can cause brake system damage - which would alert the service tech to the use of silicone brake fluid - which would mean no warranty coverage).

I think more advanced drivers could justify the potential voiding of warranty coverage - but at my level (novice to intermediate) Super DOT 4 is more than sufficient...
Note SRF is not silicon based. Silicon based is DOT 5.1 IIRC

SRF does not void any warranty, besides, I would love to see anyone visually distinguish OEM fluids from SRF
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      09-05-2019, 06:52 PM   #16
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Quote:
Originally Posted by NYG View Post
It is a ridiculous waste of money and it adds up. If you're already spending this much money on tracking, why contribute more than what is required. Your brake lines aren't connected to any other part of your car except your master cylinder and calipers. You're quite literally just flushing money down the toilet for the sake of "Well, I spend a lot as is, not going to hurt if I spend some more."

I can justify changing your tires after every event more than I can brake fluid.

If it makes you feel better to change it after every track day then by all means, go for it. Doesn't mean you're not wasting your money needlessly.
hi NYG, I don't know your track setup, how you approach track days, your pace, your tires etc. Just sharing my current approach.

It does indeed make me feel better, and that's why I do it.

when i tracked leased BMW more casually, using street tires, I replaced fluid when the car asked
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      09-05-2019, 10:29 PM   #17
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Quote:
Originally Posted by SYT_Shadow View Post
Note SRF is not silicon based. Silicon based is DOT 5.1 IIRC

SRF does not void any warranty, besides, I would love to see anyone visually distinguish OEM fluids from SRF
This is blowing my mind right now.

SRF is apparently glycol based with silicon esters which isn't infact the same as silicon based.

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Originally Posted by nicknaz View Post
It does indeed make me feel better, and that's why I do it.
All that matters in life.
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      09-05-2019, 11:32 PM   #18
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What NYG said on first reply is pretty much all. Unless one likes pulling real high braking G every session all day or like to keep pushing and squeeze out every effort for fast lap times, it would be spendy to be too sensitive about fluid condition.
Braking as late as possible surely gives one of most significant lap time improvements, but (especially for newly learning people) braking real hard would be one of the last pieces of the puzzle after mastering/at least becoming good with other basics.
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      09-06-2019, 08:36 AM   #19
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Quote:
Originally Posted by nicknaz View Post
hi NYG, I don't know your track setup, how you approach track days, your pace, your tires etc. Just sharing my current approach.

It does indeed make me feel better, and that's why I do it.

when i tracked leased BMW more casually, using street tires, I replaced fluid when the car asked
I look at it differently...I consider changing brake fluid a high risk maintenance procedure since it could potentially cause serious damage/injury if done improperly (lose brakes, leak fluid on the wheels/track, which could cause an accident/crash). It's something I DONT want to do at all, or at least at the very min. intervals required to ensure proper working condition (FYI: I also had a leased M).
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      09-06-2019, 10:09 AM   #20
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Quote:
Originally Posted by NYG View Post
Quote:
Originally Posted by SYT_Shadow View Post
Note SRF is not silicon based. Silicon based is DOT 5.1 IIRC

SRF does not void any warranty, besides, I would love to see anyone visually distinguish OEM fluids from SRF
This is blowing my mind right now.

SRF is apparently glycol based with silicon esters which isn't infact the same as silicon based.

Quote:
Originally Posted by nicknaz View Post
It does indeed make me feel better, and that's why I do it.
All that matters in life.
Unless your from the "every little bit helps" camp and you try to make an effort to reduce your carbon footprint. (Ducking for cover now lol)
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      09-06-2019, 11:44 AM   #21
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Quote:
Originally Posted by OhioRiderAaron View Post
I look at it differently...I consider changing brake fluid a high risk maintenance procedure since it could potentially cause serious damage/injury if done improperly (lose brakes, leak fluid on the wheels/track, which could cause an accident/crash). It's something I DONT want to do at all, or at least at the very min. intervals required to ensure proper working condition (FYI: I also had a leased M).
I couldn't agree more.

I am fairly handy with cars but still follow the general rule of not touching something unless it's necessary.

The thought of swapping fluid once a year fills my heart with joy and reduces unnecessary risk
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      09-06-2019, 06:20 PM   #22
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Quote:
Originally Posted by SYT_Shadow View Post
I am fairly handy with cars but still follow the general rule of not touching something unless it's necessary.
What do you think about people who go under their car after each event and put a wrench on every possible bolt and tighten it?

That could be considered the pinnacle of unnecessary touching of things on the car by some, and an absolutely necessary part of post track maintenance by others

I am not there yet, but my teammate keeps pushing me to do it, and I am starting to come around to her point of view
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