Quick question,

I know you should change your fluid after an on track session that overheated the fluid...

I have read that once the fluid has boiled, the wet boiling temperature decreases from that point forward? How is that?

Prob a newbie question, but I appreciate your insight!

 

Isn't a brake fluid change required to pass Tech Inspection, regardless?

 

well whether it is or not, I'm looking for the reasoning...I'm not sure about any rules regarding this, I'm just using the track session talk as an example

 

I've not heard that the boiling point drops after fluid has boiled once, but I suppose it's possible. However, I would be concerned that it will boil again under the same conditions, and would want to change it simply because of that. And... I would think seriously about changing to a higher wet-boiling point fluid. .i.e. SRF or maybe Motul600. My preference is for SRF. Losing your brakes to boiling is not much fun, and tends to happen at the worst possible time.

 

If you boiled it you should replace it - no debate..

But as MGlobe said:

You should also consider WHY you cooked the fluid. If you are using OEM fluid thats (a part of) the answer. You should change to something with a higher boiling point. People swear by Castrol, Motul and SRF.. I've used all three with good results. I use SRF right now over Motul last year because thats what my race shop prefers.

If you are already using one of the higher rated fluids and cooked it, then you need to REALLY MUST consider WHY you cooked it.. Something is going on...

Things to consider....
Are you cooling down before parking it? Using the pads to the bitter end?? Keep in mind that pad thickness is a factor. As they get thin, heat transfer is higher. I try to replace my pads when they get past 50%. Assuming you aren't just thrashing the brakes.

Hope that helps

 

This is clearly defined in the PCA rules for DE's, for example.

 

You should replace it, but not because of the "rules". If it boiled once, its going to boil again. You should also go to a better type of fluid (Motul, SRF, etc). Boiling the fluid does not impact the temp of future boilings.

 

Most PCA Tech forms only require a brake flush within 6 months of the event. I've never seen a tech form that requires a flush before every event, nor one that talks about prior boiling of fluid.

 

Besides a higher temp fluid, also get some bigger brake cooling ducts.

 

You need a new car, there are a couple high end D Stock race cars for sale I can guide you to.

 

http://www.suncoastparts.com/product...7brakeupgrades

http://www.amazon.com/Motul-RBF-Raci.../dp/B000AURZ08

http://www.amazon.com/Motive-Gear-01...xgy_auto_img_c

plus rs29 pagid yellow brake pads.

if you boiled brakes you would feel it and of course you do flush after that. as you are asking if you boiled them or not - most likely you did not boil them.

it just comes with time - you will start noticing how brakes start to fade a little from event to event. I flush them after 8-10 autox events when pedal starts to feel a bit too 'springy' when you slam it down. also if you sit in your car on idle and on sudden hard press down pedal just goes all the way down and hits the floor - you have to flush it. when you get air in the system it is quite obvious, if you not sure - flush it all, if it was never flushed - get it to dealer or your mechanic, you will need to have PIWIS connected to the car to flush ABS system and tell mechanic to flush clutch too - they are reluctant to do it often as it takes extra 5 min for them to waste and bleeder is awkward to reach. in regular season you will do it yourself with that bleeder kit i gave you link for. motive bleeder takes 1.5-2 liter of fluid in it for bleeding and plenty will be left.
before you bleed you use pliers to take out plastic grid from under the cap then use little syringe to suck out rest of liquid from car`s brake fluid container,then pour in new one and then connect motive hoses.

I usually do a complete flush at my mechanic`s shop in the beginning in spring and 2-3 flushes during season, i run cheap motul 600 and it works fine.
when you do flush yourself you want to stock up with brake fluid of different colors - red and blue so when you flush you use different color so you see right away when new fluid starts to go from a caliper.

and be careful with bleeders on calipers - they do not like too much force.

 

I am not sure if this really tells us WHY, but here are a couple blurbs from Stoptech:

"Overheated brake fluid can (and will) boil in the caliper. Boiling produces gas bubbles within any boiling fluid. Gas is compressible so boiling brake fluid leads to a “soft” brake pedal with long travel."

"the system should be bled to replace the fluid in the calipers every time that it is overheated to the point of generating a soft pedal. Yes, the pedal will come back as soon as the fluid cools somewhat - but the boiling point is now reduced and the pedal will go mushy at a lower temperature the next time."

From: http://www.stoptech.com/tech_info/wp...fluid_1a.shtml

So, does the boiling result in the fluid absorbing water, or do some of those "gas bubbles" remain in the fluid?

 

Tinted or dyed fluid is not necessary. Simply dump 1 liter of fluid (water perhaps) into your transparent waste bottle and mark the side of the container at the top of fluid. Then the amount of waste brake fluid you flush out will be the same as the new brake fluid you dumped into the mastercylinder reservoir. You would likely want to push additional clean thru to account for the brake line circuit as well. 1 liter may not be enough to complete the flush depending on the total system volume.

Regarding brake fluid, I think gross vehicle weight plus high horsepower has a lot to do with minimum dry and wet temperature range required. As SRF is about $70 per liter, a complete flush would be at least $140 spent to purge all of the old fluid out. Pentosin Racing works for me and is only about $10 per liter. Works well without brake ducting, and is only 3 percent lower than the SRF dry boil temp. I flush every event, so wet boil temp is not a factor.

 

A related question......I'm bleeding my brakes tonite. Prior to the last DE in July I did a complete flush. I have Motul 600.

To do a bleed not flush, how much fluid should I take out of each bleeder screw. I don't expect to see bubbles but if I do I will drain until the bubbles are gone.

Thanks in advance!

 

some info will help us understand exactly why you boiled the fluid:

1: type of car (power-weight-etc)
2: Brake setup (fluid-pads-etc..please please please don't say "stock")

this will be very telling...it looks like you drive a 951 with the boost turned up...."if" you are running stock 951 brakes with street pads and normal fluid, it makese sense you would boil it..... assuming this is the case, the easiest solution is real race hi temp fluid (500+F) and real race pads.....that tends to work well in just about all Porsches that have anywhere near stock HP...since P-cars tend to come with good brakes....