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Discussion Starter #1
I recently had the wonderful experience of boiling my brake fluid autocrossing. This has led to a fair amount of reading and pondering my options.

I am aware that my old fluid was 4 years old, so I'm certain that was a major factor. So I replaced the fluid with OEM equivalent, DOT 4LV (Class 6, viscosity 750 or less) for modern ABS brakes. Like all manufacturer warnings, ABS may not operate as intended if I do not use this fluid. However, in light of the realization that the E-differential uses the brakes constantly, boiling fluid seems like the weak link in the stock configuration of the vehicle. I was recommended Motul 660, however that is Class 4 (viscosity 1800 or less) and thus has a higher viscosity. But on the other hand....

Viscosity is most critical in cold weather, which in southern California is not a major problem. I get a 3 to 5 weeks at the most of 30 to 40 F degree weather in my area, and the viscosity test is based on -40! So I'm not certain that regular viscosity would really change how my ABS functions? So, before I make the jump to High performance brake fluid, I want to find some data to clarify this. Personal experience is always valuable, but if you can link a useful website that addresses this directly, like a test or experiment that would be most interesting.

My ABS concerns center around the fact that my car is my daily driver first, and a weekend warrior second. So reliable braking in the real world is my first priority. Remember, real world brakes often operate cold and are formulated for that. Only people who go to a track worry about high temps. So a track set up, may not be optimal for cold emergency brake on the morning commute. And yes, I'm probably over analyzing this, so be gentle. :)

My second question on High Temperature brake fluid has to do with frequency of flushing the fluid. Most websites agree that Hi-temp brake fluid needs to be changed more frequently, but I'm not clear on why. Obviously, frequent heat cycles from track use would break the fluid down, thus needing a flush/replace more often. So that's my primary thought. However, I see two conflicting responses on the internet. Some sources say that Hi-temp fluid absorbs moisture more quickly, but no data is provided. Then to conflict that, nearly every product claims their fluid is formulated to resist moisture absorption and vapor lock. I don't mind changing the fluid, I just want to know why with a logical and scientific explanation. Once again, personal experience is appreciated, but if you can link a good source for some... light reading... I'd like that very much.
 

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... I don't mind changing the fluid,....
If changing the fluid isn’t a concern then why not run an OEM recommended fluid unless you’re at the track?

Why not change the fluid over to a racing fluid on track days?

It would be awesome if you shared the empirical data you find that satisfies your question.

But I agree with your instincts in that you’re over thinking it...especially since your car lives in SoCal.

You can run a Motul 660 like racing fluid year round - just change it every 9-12 months.

If running a racing fluid year round makes you uncomfortable, then change the OEM style fluid to a racing fluid before you track it.
 

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Discussion Starter #3
But I agree with your instincts in that you’re over thinking it...especially since your car lives in SoCal.

You can run a Motul 660 like racing fluid year round - just change it every 9-12 months.

If running a racing fluid year round makes you uncomfortable, then change the OEM style fluid to a racing fluid before you track it.
I think I just want to know the science. Ultimately, I am going to run the OEM right now to see if it will boil again. I'll carry a bleed kit with me this time incase it happens. If it does, then I will switch to the Motul or an equivalent and begin testing on my own if I can't find the answers.

Another interesting issue I discovered is chemisty/solvency. Some online comments indicate that switching types of fluid can cause seals to fail. Yet each manufacturer I am looking at for fluid, claims their product passes rubber compatibility. But there are many rubber formulas depend on car make or year of production, plus whether or not the commentor properly maintained their vehicle. Once again, I'm certain I"m being OCD, but I love knowing "why?"
 

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Discussion Starter #4
So I am not an expert, engineer or anything like that. I'm just an ethusiast trying to figure this stuff out. So having said that...

This is the best article I have found on fluid performance by brand and quality levels. What surprised me was that despite the knowledge that race fluid is very hydroscopic, it was similar to (BMW) OEM fluid. So perhaps it's the bigger influence is the heat cycles of autocross/track use breaking down the fluid faster than daily driving.


Regarding viscosity, I found this article. About half-way down is a chart that show (Oil?) viscosity vs. temperature. Assuming brake fluid is similar, it seems fluid remains very thin until you pass a critical freezing point and then it begins to thicken rapidly. If this is true, for my temperature range running regular DOT 4 will have no impact/change to my ABS system. I will try to find more, but this is what I have so far.

 

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Discussion Starter #5
Here's an engineering article on Heat soak of brake fluid after you park the car from hard braking. At roughly 30 to 60 minutes brake fluid heat soak peaks from being parked, reaching 200 to 350+ degrees depending on variables. The example used is for mountain braking, but for my purpose of autocross it should be the same. This means that OEM brake fluid wet boiling point can easily be exceeded for my second set of runs which I experienced. This also means I might not need High temp brake fluid as long change it more often keeping me closer to the Dry Boiling point. So far I have not made a final conclusion as to what is best for my needs. But it is all very interesting. If only I had an engineer in Fluids and Mechanics to talk too...

 

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Discussion Starter #6
My next research topic is how often High temp brake fluids need to be changed. Some sources say as often as two weeks, or even the same day under heavy use at a high speed track for instance. Others say once a year with street use. Most say depends on brand and use. Additionally, as the fluid heat cycles from hard use it essential becomes cooked and (may) darken. This cooked fluid is more prone to aeration and moisture absorption, I am assuming. I have not posted these sources, because it's a lot of reading and many are secondary quotes that give the original source for verification.

So I did a search for Motul, as that is one brand I am interested. I found this vendor explanation, comparing Motul 5.1 to 600. For the record, vendors are trying sell stuff, so I generally assume they are painting the product in the best light. My advice, search your brand directly with key words like "moisture absorption". And be prepared to sort through the many vendors that offer no useful answers on real world application. And take everything on the internet, including my posts, with a bit of caution as they could be misinformation, biased or out of date. Please add to this thread if you have good information, a good online source or personal experience with specific conditions your can describe.

 

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Discussion Starter #7
So I just ordered Motul RBF 600 and plan to bleed the brakes and clutch after the holidays for my next autocross. Once done, I will "test" the ABS on a cold morning, note the temperature and how the ABS responds. I am predicting, since the lowest the temperature we get here is around 32 F, ABS will operate fine for my needs.

My long term test I suppose should be those test stripes and take monthly readings of the water content in the Motul.
 

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interested in results of water absorption..
 

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Discussion Starter #9
Update: I bleed the brakes (and clutch) today with motul 600. I then went for a test drive. Brakes feel like I'm getting more pedal feedback. Hard to explain, but I could briefly feel the rotor passing across the pad while braking around a corner at low speed. ABS seems to work. 68 F, so it is warm. But it does feel different. With the low viscosity it's like a bunch of little pulses. With the Motul, it's like several larger pulses. Does it work well? The candy wrapper in the back seat that flew past me out the window when the ABS went into action definitely surprised me! But I'm not sure that's "objective science."

The real tests are as follows:

1) Cold mornings? Will ABS work correctly down to 32 F, the coldest it gets in my area. I should have an answer by the end of February.
2) Will it damage the ABS unit? Only time will tell. I'm thinking if it did, someone would have complained by now.
3) Will the 600 noticeable help in autocross, beyond thermal resistance? I'll report back after Sunday. :)
4) Will the 600 contaminate faster than regular brake fluid, with once a month autocross? I need to order some test strips and begin testing monthly to data record.

As a side note regarding bleeding the clutch. Yes the clutch on this car can be tricky to bleed. But this was my second system bleed and last time I did the brakes only. Contaminants were being siphoned from the clutch into the brake system. The clutch fluid was icky! So if you are up to it, I recommend bleeding the clutch. That being said, many have posted having difficulty doing it, so do your research. I used a Motive Pressure Bleeder and topped off the reservoir before I began. I believe Ford designed the system for a reverse pressure bleed which is why so many people get air in the clutch lines. But now I'm off topic on my own thread...
 

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Discussion Starter #10
Autocross update: Brakes felt great today! When it was cold, mid-40's, the stock brakes felt grabby on the first run, like when the car was new. During the rest of the runs the brakes worked consistently and dependably, with no significant tapper off with each run. There was one run I thought the brakes were letting me down, but then I realized that I had left TC on, so that was my fault. The following run was my best time of the day once I turned the TC off. ;)

ABS worked fine from mid-40's up to upper-60's just fine with no problems. All speeds were 2nd gear. ABS is more noticeable now, as the pulses feel more assertive.
 

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Good to know! (y)
 

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Discussion Starter #12
I have driven 20 laps over 2 autocross events since putting the Motul 600 in. In the beginning the Motul felt amazing! Now it feels like regular brake fluid. While driving home today the brake pedal felt a little too much travel. I took a look at the fluid and it has a dark honey color, instead of the light clear yellow. I'd hoped peak performance would last longer. Our cars with the E-diff is just brutal on the brakes. I'm sure it doesn't help either that I don't take cool down laps, especially after the final lap. I'd also like to note that the ABS seems harder to trigger now. Like I really have to put my foot into it and the response is "chunk-a-pulse-chunk-a-pulse" like the fluid it too thick even in warm weather.

I am debating over going up to a 650 to 700 type fluid or stepping down to an inexpensive but good fluid like ATE 200. A higher heat tolerance may help, but Motul 600 is no wimp -- especially for autocross. And no fluid will prevent water contamination from finding it's way into the lines. I mean we actually did have rainy weather this year in California. Stupid molecules!!! Which makes me think if I have to flush frequently to maintain peak brake pedal feel, a cheep but good fluid is my best bet.
 

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Good thread. I stick to FoMoCo specs due to blind faith that the good people developing Ford Performance cars did their research and analysis. That being said I am 99% sure I boiled fresh (<1 day old) DOT4 LV with a dry boil over 500F. Equivalent spec to Motorcraft DOT4 LV. My next track day will be all about heat management, and if I can get into brake upgrades for cheap I will. I have tires beyond my skills, Im stock and will admit I have power beyond my skills, I need brakes well beyond my tires and power. I am thinking of starting with track pads, ducting, and wonder if a better, non-LV fluid with an extra 100+ dry boil temp will help. If it's literally just cold ABS/TCS I will ditch the LV in a heart beat. I will also admit my mistake, my first 20min session I left all nannies on and overdrove the car. That is typical autocross behavior. That was a mistake.
 

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Discussion Starter #14
@GammaRadiation I can tell you that the first Autocross after I switched to Motul RBF 600 it was AMAZING! There was a tiny drop off at the end, but nothing significant. The second event the pedal has lost its firm sharpness, but everything worked and it never boiled. While driving home last friday I noticed some extra travel in the pedal. Nothing serious, but it made me curious. After two months and 2 Autocross events the almost clear yellow fluid now looks like a darker honey. The brakes on these ST's get HOT. With the nannies on, it's terrible. But with them off, the E-diff still interferes for good handling, however hard on the brakes. The brakes are just being asked to do too much. I'm plan to do one or two more events before I bleed out the Motul just to see how months and events it can stand up to. Right now I have two months and 20 runs and I'm just noticing the slight softening of the pedal (which still feels better than most people's car who never change their fluid).

I was advised to do cool down laps after my runs to avoid "heat soak" into the caliper. I might start doing that. I figured the Motul 600 would be pretty invincible, but now I'm realizing that even with a good fluid heat KILLS. Especially as a novice who is probably overdriving every corner. I am more likely to brake too late than too early.

My current thoughts right now is that it is more important to get seat time in and change brake fluid frequently, than drop money into brake, since the pads and rotors themselves seem fine. I understand that track speeds are much faster than autocross, which means your heat will be MUCH higher. Perhaps run the high temp stuff for the track and then bleed it out with affordable Dot4 LV for the daily drive? I mean if you're going to bleed frequently... wait that came out wrong... you get the idea.

I will say one thing, while I am learning what works for me and what doesn't work, among my tools that I take to autocross is a bleeder kit and fluid in case I do boil the fluid again. I'd like to finish my runs and drive home too. And add couple spare tires too if you have them. I seen a guy cord his tires at the beginning of the event and he couldn't take the rest of his runs. :(
 

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The track I was at is known to be hard on brakes. Apparently race teams are now using it specifically for testing brakes. It's also the most accessible and least expensive track for me. While I am a proponent of driving the equipment you have until you find its limits, I think I found those limits. I think I'll just better enjoy my time out there, be more relaxed, and therefore learn more if I have more brakes. Pads and ducting shouldn't cost too much, so that's a good place to start. I like your tip about bringing a bleeder to the track, I think if I could have bled during lunch I would have had better afternoon sessions.

Anyway, if there truly are no Ill effects from non LV fluid in warm climates it's what I will switch to. I'm in Florida, I run summer tires year round, why not run "summer fluid" year round as well? :cool:
 

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Discussion Starter #16
"if there truly are no Ill effects from non LV fluid in warm climates it's what I will switch to."

Well that's what I'm testing. I largely agree with your philosophy of trusting the OEM engineers, but after boiling my fluid I'm now experimenting. I will be amused if in a year from now I come full circle back to OEM and frequent changes. ;)

I will say this though, the ABS feels different, so I know the viscosity is thicker in the non-LV. And what I"m finding interesting also is that as the Motul breaks down it feels like the ABS is harder to activate unless I bury my foot in it.

I just ordered some ATE Type 200 to try next. LV has a viscosity of 750. Motul 600 is 1750. More than double. The ATE is 1400. I think this thread is going to turn into the trials and tribulations of my experiments in brake fluids on a budget.
 

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I've been pouring over spec sheets and all I can find is the FoMoCo LV kinematic viscosity spec is much lower at very cold temperatures (-40C).

At 100C Motul RBF 600 has a lower kinematic viscosity than LV at 40C. Density is also very similar. Thus, if ABS and TCS works with cool brakes on a warm day it should work fine with Motul and hot brakes on the track.

If you live in a very cold winter climate I would play it safe and flush factory spec LV when you put on your snow tires. For me, my car will never see temps much below 0C. Because I run summer tires year round I also don't drive the car hard at those temps until everything has heated up. Thus, I'm making the switch to Motul for track days.

Report back, I'll do the same if I notice any negative affect.
 

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Discussion Starter #18
I had an epiphany today. I was thinking about my last event and how the car was struggling to stop for the tight 120 degree turns from 60 mph. With the Motul 600 and my increasing experience I'm braking later and harder before my turn. What if the Motul is relatively fine, but now that I have a quality fluid I am now exceeding the heat range of the OEM brake pads?


After reading this, I believe brake pads are my next upgrade. But I need to know the temperature range of our OEM pads to make a proper choice. Anybody know?
 

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Discussion Starter #19

Our OEM pads seem to be FF in the front and FG in the rear. This is based on photos online shown by web users selling the pads. The rear surprised me until I thought about how the rear can lock up to induce oversteer. Clever Ford engineers...

The fronts have a strong intial bite but fade at the top end of their temp range. I'm guessing the FF range is something like 0.44 from cold to 250 F, and 0.36 as you hit 600 F.

So the rear pads should be fine to be left alone. But the fronts need some upgrades. For me I'm looking at HP+ Hawks or Carbotech 1521. I'm leaning towards Carbotech, for the modulation everyone claims and the rotor friendlyness (if there is such a thing with a higher performance pad). The AX6's are just too loud for my preference.

But wait, what does this have to do with Brake fluid? Well the right pad means less time with my foot in the brakes, so I'm hoping by slowing down faster it will actually generate less heat soak and a new pads should insulate the caliper more effectively than my half used OEM pads. So yes, proper pads should help with brake boiling/degradation. In theory. I need someone with more experience to comment to confirm if I'm heading down the right path or arm chair racing.
 

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OEM spec rotors are cheap, so if there is a streetable pad that is also decent on the track that's what I want, rotor wear and brake dust are not an issue for me. I reblend my brakes with LV fluid because I had some left over and for the most part everything seemed fine...except my rotors are trashed and the pads have significant wear.
 
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