Here's my take...

I have a DE coming up in a few weeks and was thinking of having the brake fluid bled to ensure there wasn't any air present. The fluid is Castrol SRF and was installed in April.

I checked with the shop that would do the work and was advised that the best price they can find on this fluid is $75/L; by comparison,Motul runs about $16/500ml.

I have difficulty spending $75/L knowing that a small fraction of the liter will be used.

Can another brake fluid be used in the bleeding process--like Motul 600--without adversely affecting braking performance?

the fluid you will run to bleed it will nter the reservoir and maybe get as far as the MC. The only place we are concerned with boiling is in the caliper cavity itself. So the new, lower quality fluid will not be very near the calipers in theory.

However, NEXT time you bleed it will have migrated into one or more of the calipers (maybe). If your next bleed will be a flush, who cares.

I dont know if all fluids are compatible with SRF. I assume they are.

I also wonder if SRF is really needed outside of racing. I measure my caliper and rotor temsp and never get over hgih 200s F, well within the performance of ate super 200, pentosin DOT4+, and for heaven's sake, castrol GT-LMA.

We'll await the good doctor's answer.

Grant

ps: hello!

Grant:
Thanks for the reply.

SRF is probably overkill for my DE application but I have to say at the DE we attended, with out side temps in the 90's, I had no fade whatsoever running a set of rotors that were almost done and pads that were around 60% I was really impressed with this fluid.

I'm thinking of just bleeding with Motul 600 to ensure there aren't any air pockets; I hate to spend that kind of $ on a bottle of fluid knowing I'll just use a small % of it.

On the Rennilist, some guys keep this stuff in for years and just bleed it annually; I'm not sure I'd be ok with that, living in a pretty moist environment, but I'm looking just to get through the rest of this DE season and then decide if I stick with it or go back to Motul.

look at the wet vs dry boiling points. I dont have them memorized, but i'd make a small wager and feel safe :-)

the brake system. It is not air in the braking system you are so much worried about -- or if you are worrying about it you are worrying about the wrong thing unless the pedal is mushy/spongy -- it is the water in the old brake fluid. When the fluid gets hot its boiling temp is lowered with the water present. The result? While the brakes are firm cold they get mushy when they get hot which is most disturbing when you're in the heat of the run and come upon a corner a bit too fast and find the brake pedal soft...Scary.

A few dollars of brake fluid is a small price to pay for helping to guarantee your car's braking action is proper not only on the street but on the track as well.

If you DE, auto-x or track your car skimping on brake fluid and brake fluid flushes/bleeds is false economy and unsafe.

Sincerely,

MarcW.

thanks for all the replies.

The fluid was replaced in April, I've had no spongy pedal to this point but have thought about the bleeding just to ensure that I haven't gotten any air in the system since the DE.

Here are some comparisons on various brake fluids; check out the SRF wet boiling point:

Fluid type Fluid description Dry/Wet Boiling Point Size/per bottle Price/per bottle
ATE Super Blue/TYP 200 Super Blue is a very high performing brake fluid. A mainstay in German automobiles, Super Blue is arguably the best value for your money in brake fluid. Dry: 280°C (536°F)
Wet: 198°C (388°F) 1 Liter $19.95

Brembo LCF600 LCF600 is the newest brake fluid on the market. Excellent choice for track use. Proven low compressibility. It gives a firmer pedal feel then most other brands. Dry: 316°C (601°F)
Wet: 204°C (399°F) 16.9oz/ .53 quarts
.50 Liter/ 500ml $19.95

CASTROL SRF The SRF is the absolute best brake fluid on the market, period. If you want the best the Castrol SRF is it. Due to it's extremely high dry & wet boiling points. Dry: 310°C (590°F)
Wet: 270°C (518°F) 1 Liter $79.95

MOTUL RBF600 The world's best selling brake fluid. Developed for all forms and levels of racing, the RBF600 is one of the most popular fluid's on the market today. Dry: 312°C (594°F)
Wet: 216°C (421°F) 16.9oz/ .53 quarts
.50 Liter/ 500ml $22.50

The SRF wet boiling point is nearly as high as the ATE dry boiling point, and since the fluid has only been in since April, I'm not terribly concerned about water absorption to the point of affecting braking ability.

Having said all that, the Motul looks to be the most cost effective.

leaks in brake hydraulic systems are not normal nor something that should be lived with or tolerated.

If you have no reason to suspect air the goal is to introduce fresh brake fluid to flush out the old fluid that has accumulated water (from moisture in the air). This happens and is why Porsche recommends 2 year brake flush/bleed intervals.

This 2 year number is ok for cars driven on the street. But for cars that see harsher usage, more demanding usage the 2 year interval may find the car undergoing more demanding usage with brake fluid that has too much water in it and in this case too much water is any water. The result is the fluid boils at a lower temperature than it would otherwise and of course is raised to a higher temperature than it sees on the street. The result is a spongy pedal but one that comes on suddenly, unexpectedly, and in a DE or track event almost guaranteed to be at the most inopportune time.

As for brake fluids I can't say which is best. All I know is DOT 4 fluid should be used to I guess to be compatible with the brake system internals and compatible with the bit of old fluid left in the system. This includes the ABS system which is not always flushed when a home DIY'er flushes/bleeds his car's brake system.

Sincerely,

MarcW.

... all of those high-performance brake fluids are good.
But I follow my own strict rule: Replace ALL the fluid before every DE.
Since I run 10 DEs per year I look for the best bang-for-my-buck product which is ATE.
I've never had brake fade following my rule.
Since replaced the fluid in April and haven't done any DEs since then, you should be good to go.
You would have to be really fast and aggressive driver, at a very hard-braking course in a very fast racecar, on an extremely hot day to need anything beyond 280°C (that's 536°F).
The rotor's temperature doesn't transfer directly to the caliper.
The temp is generated between the rotor and the pads.
Eventually, with time the caliper will start heating up and finally the brake fluid.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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