Brake Fluid Flush - How Often?

[Powerslide]

Does anyone use a "rule of thumb" in terms of how often you change brake fluid? This summer I've only done one track day (4x25-30 minutes sessions) - and that was after replacing brake fluid (stock brake fluid).

Is there a certain amount of sessions or track days after which fluid should be replaced? I'm especially interested in those who are using stock fluid (my service department said BMW has a service bulletin saying that silicone-based brake fluids are not covered under the manufacturer's warranty)...

Any suggestions are appreciated,

[kitesurfer]

I am guessing your not an advanced HPDE driver as you probably already know of the benefits of Castrol SRF. You should be fine with OEM Brake fluid, as good rule of thumb is to bleed the calipers before each event or after a couple events (if you notice a soft pedal), Getting fresh fluid into calipers (especially fronts) is all you really need during the season. However I would definately do full brake fluid change once a year if you plan on tracking

[Gstone]

I am doing my first HPDE in 1 month. My M4 is 2 years old 13Kmiles. Just had oil service and just scheduled first brake fluid flush at BMW ($220 quoted) to be done before HPDE.

[FLOSS M]

I use Motul 600, bleed all corners before each event. I like having fresh fluid at the caliper.

[afadeev]

Originally Posted by Powerslide

Does anyone use a "rule of thumb" in terms of how often you change brake fluid? This summer I've only done one track day (4x25-30 minutes sessions) - and that was after replacing brake fluid (stock brake fluid).

Short answer - if you do DEs, at least once a year, usually in the off-season.
Longer answer - it depends on the fluid, and the intended application.

There is nothing wrong with stock brake fluid if you couple it with track pads (e.g.: RS29s). You can alternate free OEM brake flush that's due every other year, with one of your own (Castrol SRF, Motul 600).

If you are doing club races, consider flushing before each and every race.
For DEs, doing a full fluid flush before each event is a bit of a waste of time and money.

Originally Posted by Powerslide

Is there a certain amount of sessions or track days after which fluid should be replaced?

Brake fluid is hygroscopic, which means that it absorbs moisture out of the air overtime. Increased water content in the brake fluid lowers the boiling temperature point of the mixture. If you exceed the boiling point, fluid turns into vapor, and your brake pedal hits the floor without engaging calipers/pads to slow the car down. Then your underwear turns brown.

Water boils at 212F.
Basic DOT 4 brake fluids have boiling point in mid-300F / low-400F range.
Track brake fluid (e.g. Motul 600) has a boiling point of 594F.

The real benefit of higher boiling point is not just the numbers starts high by itself (you are unlikely to heat your fluid THAT much), but that it buys you more usable time even as water gets absorbed into the brake fluid. Specifically, Motul 600 has the "wet" boiling point of 401F. That's as good or better than most fresh DOT 4 fluids:
https://www.motul.com/system/product...pdf?1340122148

Originally Posted by Powerslide

I'm especially interested in those who are using stock fluid (my service department said BMW has a service bulletin saying that silicone-based brake fluids are not covered under the manufacturer's warranty)...

Silicone-based brake fluids are usually classified as DOT 5.
You don't want those, as they can damage rubber seals. DOT 5 fluids also don't work well with ABS pumps.
Silicone fluids are also hydrophobic, so as moisture gets into the system, it will form puddles of water, which will be the first to boil and turn into vapor when heated. Very undesirable for track driving.

Stick with DOT 4 fluids, and consider buying more water absorption time with high-performance fluids cited above.

HTH,
a

[CanAutM3]

I've been sucessfully running the stock brake fluid on all my ///Ms over the past 16 years at the rate of 16~20 track days per year. I have the fluid flushed every spring just before the start of the track season.

[kitesurfer]

I will say this if you plan to run an aftermarket fluid, Their is a reason why almost every race team runs Castor SRF, Its wet boiling Performance Delta is so far beyond any other fluid in the market.

[aboulfad]

Originally Posted by CanAutM3

I've been sucessfully running the stock brake fluid on all my ///Ms over the past 16 years at the rate of 16~20 track days per year. I have the fluid flushed every spring just before the start of the track season.

ditto, to the part of changing with stock brake oil once per year or beginning of season. That's what BMW also recommends in their track document preparation list for the M.

[Powerslide]

Originally Posted by CanAutM3

I've been sucessfully running the stock brake fluid on all my ///Ms over the past 16 years at the rate of 16~20 track days per year. I have the fluid flushed every spring just before the start of the track season.

Aside from flushing the fluid every spring - do you ever bleed fresh fluid into the calipers before each driving session like others have posted?

[CanAutM3]

Originally Posted by Powerslide

Aside from flushing the fluid every spring - do you ever bleed fresh fluid into the calipers before each driving session like others have posted?

Never had to.

I guess it boils (pun intended ) down to how much brake OCD you have. Some folks can only live with a "rock hard" pedal and can go through tremenduous expense to achieve this. IMO, it is perfectly normal for the brake pedal to need a little more travel when on track. As long as I have full braking power, good modulation capabilities and that the pedal never goes close to the floor, I don't mind the additional travel. Saves me a lot of hassle and does not hurt my lap times .

[M3 Number 86]

Originally Posted by CanAutM3

Never had to.

I guess it boils (pun intended ) down to how much brake OCD you have. Some folks can only live with a "rock hard" pedal and can go through tremenduous expense to achieve this. IMO, it is perfectly normal for the brake pedal to need a little more travel when on track. As long as I have full braking power, good modulation capabilities and that the pedal never goes close to the floor, I don't mind the additional travel. Saves me a lot of hassle and does not hurt my lap times .

If you're used to it it should be ok but note that consistency will go down for others.

[aboulfad]

So today on my local tiny track, a Porsche 911 Turbo brakes went limp and the beginner driver was complaining that he should have had "racing" brake fluid. I, on the other hand, another beginner and haven't experienced any brake fade with the BMW brake fluid in any of my sessions.

Is there any link between the type of brake fluid used and the brake pedal travel/fade?

[CanAutM3]

Originally Posted by aboulfad

So today on my local tiny track, a Porsche 911 Turbo brakes went limp and the beginner driver was complaining that he should have had "racing" brake fluid. I, on the other hand, another beginner and haven't experienced any brake fade with the BMW brake fluid in any of my sessions.

Is there any link between the type of brake fluid used and the brake pedal travel/fade?

Fade is often split into two categories: friction fade and fluid fade.

With friction fade, the pedal remains firm but there is a progressive loss of braking power. With fluid fade, the pedal needs a progressively longer travel to generate the same brake force. The danger with the later is that there comes a point where the pedal goes to the floor and the car does not stop.

I consider a slightly longer pedal to be normal at the track. As long as the pedal travel does not keep getting longer (fluid fade), that you still have full braking force and that you can still finely modulate the brake force, I don't see this as detrimental. As I posted earlier, some folks want that rock hard pedal just as they have on the street. It can be quite costly to achieve this without any true gain in performance.

Maybe it is just that that the 911TT driver experienced.

[YMB_M3]

Originally Posted by aboulfad

So today on my local tiny track, a Porsche 911 Turbo brakes went limp and the beginner driver was complaining that he should have had "racing" brake fluid. I, on the other hand, another beginner and haven't experienced any brake fade with the BMW brake fluid in any of my sessions.

Is there any link between the type of brake fluid used and the brake pedal travel/fade?

If you're not getting any symptoms of a soft pedal on oem Bmw fluid and DSC on you need to drive faster, much faster!!

[CanAutM3]

Originally Posted by YMB_M3

If you're not getting any symptoms of a soft pedal on oem Bmw fluid and DSC on you need to drive faster, much faster!!

Give him time

[aboulfad]

Originally Posted by YMB_M3

If you're not getting any symptoms of a soft pedal on oem Bmw fluid and DSC on you need to drive faster, much faster!!

All in due time you gotta walk before you run!

[HP Autosport]

Originally Posted by kitesurfer

I will say this if you plan to run an aftermarket fluid, Their is a reason why almost every race team runs Castor SRF, Its wet boiling Performance Delta is so far beyond any other fluid in the market.

With SRF you just need bleed enough just to get the air out before the next track day. Flush before the next track season. All the other fluids you will need to flush much more often.

[CanAutM3]

Originally Posted by HP Autosport

With SRF you just need bleed enough just to get the air out before the next track day. Flush before the next track season. All the other fluids you will need to flush much more often.

I guess it depends...

As I posted earlier, I use the stock fluid and flush once a year in the spring and never had a need to bleed in between. I have been doing that for the last 16 years with my 3 ///Ms at the rate of 16~20 track days per season.

[HP Autosport]

Originally Posted by CanAutM3

I guess it depends...

As I posted earlier, I use the stock fluid and flush once a year in the spring and never had a need to bleed in between. I have been doing that for the last 16 years with my 3 ///Ms at the rate of 16~20 track days per season.

If you are not exceeding their operating temps you are good, otherwise you should simply for the higher dry/wet boiling temp of a fresh fluid.

[wakdady]

"rule of thumb?" two year intervals.
along with your microfilter, lol

[HP Autosport]

Originally Posted by wakdady

"rule of thumb?" two year intervals.
along with your microfilter, lol

Every two years if you don't track your car or boil your fluid with weekend canyon runs.

Micro filter will vary greatly. Dusty area obviously more often than the recommended intervals. After a forest fire with all the ashes, replace it right away.

[Acturater]

I'm thinking of doing my first HPDE in a couple weeks. How much braking on average would you say you split between engine braking and pedal braking?