Toyotec's How to understand brake fluid and Super DOT 4 data comparison table

Discussion in 'Track Prep & Tech' started by Toyotec, Dec 31, 2013.

  1. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Introduction

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    Ever wonder what your brake fluid does? Or why on that trackday the brake pedal went to the floor, after parking up in the pits from giving it some large. Please read on.

    Besides acting as an incompressible hydraulic medium, to actuate the pistons of the braking calipers or brake drums, from the brake pedal and master cylinder, brake fluid has other responsibilities, such as corrosion protection, lubrication of brake system components and the ability to withstand heat without becoming compressible, which in turn creates a spongy pedal feel or no pedal at all!
    Vehicle brake fluid falls into two main categories, which are, fluids that contain Silicon and fluids that contain Glycol Ether. Fluids containing Glycol Ether are more widely used and are the only fluids that should be used in racing brake systems.

    Silicon based fluid (DOT 5)

    Brake fluids that contains silicone, are commonly used in military type vehicles. Also some show cars use silicone based fluids as it does not damage painted surfaces. Silicone based fluids are regarded as DOT 5 fluids. Silicone based DOT 5 was originally introduced to give higher temperature performance over Glycol based DOT 4. In comparison to DOT4, they are more compressible and can give the driver a feeling of a spongy pedal.
    Silicone based fluids are non-hygroscopic meaning that they will not absorb or mix with water that is usually present in a brake system. Because it does not absorb water, any water remains as globules, which can pool in low spots in the system and cause corrosion. As water boils at approximately 100 C and the braking system can achieve temperatures much greater than this threshold, the ability of the brake system to operate, as the system temperature increases, quickly degrades, and the steam created from boiling water adds air to the system, leading to a spongy pedal and a decrease in brake efficiency. This is why silicone brake fluid lacks a responsive feel, in comparison to Glycol based fluid and is not to be used in motorsport applications.

    DOT 5 silicone fluids is also poor lubricant and does not lubricate ABS pumps as well as Glycol based fluids. It therefore requires special design considerations if used in braking systems.

    Silicone based fluid must never be mixed with Glycol Ether based fluids.

    Glycol based fluids (DOT 3, 4, Super DOT 4 and 5.1)

    Fluids containing glycol ethers are regarded as DOT 3, 4, and DOT 5.1. This is the type of fluid we run in our VWs. These type fluids are hygroscopic meaning, they can mix with water and still have acceptable performance. The absorption of water will does reduce the boiling point of fluid, leading to the terms Dry Boiling Point (DBP) and Wet Boiling Point (WBP)

    DBP Boiling point without water absorption
    WBP Boiling point when water absorption has passed a %/volume threshold.

    DOT3/4/5.1 fluids are about 2 times less compressible than silicone type fluids when heated. This leads to a responsive pedal feel, which can remain durable, throughout repeated heavy braking, when there has been sufficient time for heat to be transferred to the fluid. Because Gycol Ether fluids do absorb moisture, it is recommend to change the fluid on a regular basis, which in turn will maintain durable performance of the brake system.

    The DOT Brake Fluid Classification.

    The American Department of Transportation (DOT) classifies brake fluids to defined specifications.
    These specifications relate to their boiling points and chemical composition. All currently available brake fluids are covered by one of the following specifications; DOT3, DOT4, DOT5 and DOT5.1.

    The minimum boiling points for these categories are in the table below:

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    Super Racing DOT 4.

    For many of us driving track cars, our brake temperatures can exceed, those of a road car (on track), particularly when using brake pads with increased friction properties.

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    This requires a fluid that has higher than normal boiling points. This is where the Racing Super DOT 4 range of fluids come into the picture. These fluids are compatible with DOT3/4 and 5.1, but have Dry Boiling points that exceed the best 5.1 or regular DOT 4. One downside is usually cold viscosity at -40 deg C which can be more than 1200 centistokes compared to just 900 for DOT 5.1. Note at room temp of 20 deg C, viscosity is ~ 20 centistokes (mm^2/s)

    The Racing DOT 4 comparison data table

    It has often been asked on this forum, which brake fluid is best for my track car. I have complied a table to show the comparison in terms of price for the Super DOT 4 fluids that are available on the market today.

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    One the best all round fluids on that chart is the ATE Super Blue. Responsibly priced and spec'd to meeting the requirements of most spirited trackday drivers. One the best and most expensive is the Castrol React SRF Super. Even with a Wet BP you can still outperform the best DOT 5.1 system.

    Hope this helps the next time the question is asked.

    Toyotec :thumbup:
     
  2. Tristan Forum Junkie

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    Ed, that's just fantastic. Take a bow, good sir!
     
  3. Nige

    Nige Paid Member Paid Member

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    My brakes run rather hot at times too...
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    Hot enough to melt the dust caps !
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    I run ATE Superblue and have had zero issues with the fluid boiling. A agree with Eddie, for the money it`s great stuff :thumbup:
     
  4. tshirt2k

    tshirt2k Forum Junkie

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    I changed from 5.1 to Ate Superblue and got a pedal back.
     
  5. vw_singh Events Team Paid Member

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    Great thread Eddie. I only suffered brake fade one at Bedford recently and that was when using Halfords Dot4 racing. Pedal feel was ruined until the fluid was changed. Turns out it's absorption rate is quite high leading to a short life span. Now on Super Blue. Yet to see how long it lasts.

    Gurds
     
  6. mr.brown

    mr.brown Paid Member Paid Member

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    Excellent work Eddie.

    FYI, ATE SuperBlue with CGTI discount works out at 11.46 per litre from GSF.


    "DOT3/4/5.1 fluids are about 2 times less compressible than silicone type fluids when heated. This leads to a responsive pedal feel and remain durable, even though the fluid has absorbed some temperature. Because Gycol Ether fluids do absorb moisture, it is recommend to change the fluid on a regular basis, which in turn will maintain durable performance of the brake system"

    Should that be moisture? You can tell I actually read the whole thing :)
     
    Last edited: Dec 31, 2013
  7. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Changed the sentence after reading again. Yes I was referring to heat. Thanks for picking that up.
     
  8. tshirt2k

    tshirt2k Forum Junkie

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  9. DEX

    Dex Paid Member Paid Member

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    Awesome post Eddie :thumbup:

    Possibly some more info to contribute...

    Halfords Performance Dot 5.1 is listed as 269 deg C dry and 187 deg C wet. (so lower than the Super DOT 4 Fluids) but it has the lower viscosity. I understand that some cars with ABS prefer 5.1 to Super DOT 4 since the thinner viscosity/lighter fluid allows it to react more quickly to the cyclic rate of the ABS.


    One other thing to bear in mind is that the longer you leave the fluid in the car, the more moisture it will absorb as well as dirt and particles from the brake system. If you've spent 40 on a litre of brake fluid you're more likely to resist changing it, while Halfords 5.1 at 13/litre (or even less with a trade card) can be changed 3 times as often.

    The Castrol SRF is a bit of an oddity in this respect as it's wet boiling point is so good (as good as the dry boiling point of the Halfords 5.1) but something like the Motul fluid at 32-34/litre will soon see it's boiling point drop as it absorbs moisture compared to a cheaper fluid changed twice as often.
     
  10. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    I did not cover specific DOT3, 4 or 5.1 in the comparison and focused on Super DOT 4 brands, as they tend to exceed the BP of all classifications.

    Historically silicon based DOT5 was used to achieve higher BPs that could not be achieved by DOT 3 or 4. Now with a modern Gycol Ether chemical structure, we can achieve DOT5 level performance with water absorption hence the DOT 5.1 classification. Indeed the DOT5.1 also has better cold viscosity to -40 deg C at no more than 900 centistokes ( similar to some DOT 4 fluids) , However at the other end of the scale at 100 Deg C they all tend to be around 2.5 centistokes.

    All the Super DOT4 systems are compatible with ABS systems, although some fluids are not recommended if your system has magnesium.

    On the subject on water absorption, you are advised to replace your fluid at manufacturer intervals or at the interval recommend by the brake fluid supplier, which ever comes first.

    I do not know what is the rate of water absorption between fluids, but I do know on some what is the saturation point before switching to WBP status for:
    Castrol React SRF stuff does have a wet BP water absorption threshold of 1.5% of weight ( 18 month change interval)
    Compared to Halford Super DOT 4 of 4% ( 24 month change interval)
    I do not know what was the absorption threshold for ATE stuff, but the the change interval is 36 months before switching to WBP status.

    :thumbup:
     
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  11. Peter Jones Forum Member

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    I'm using the AP 660. It's dear as poison but works very well.
    The brake system was all new so I decided to use top end fluid from day one to avoid any cross contamination issues if I chose to upgrade fluid later on.

    I'm very conscious of water absorption and test the fluid before each race with one of these gadgets.

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    I'm in a pretty dry climate and haven't seen any moisture getting into the system at all.

    That said, I'm flushing the front system about every 4th meet and the rear system annually.

    The clutch system I just run Castrol 5.1 as the AP would be overkill.
     
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  12. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Thanks for that Peter.

    These testers are only 15-20 and possibly a good little tool for the trackday prep tool kit.
     
  13. DC75

    DC75 Forum Member

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    great thread Edd, have used Rock oil dot 5 in the mk2 for a couple of years now with goodridge hoses and 280mm brakes(mk3 rears), always had a great feel and quite reliable when running the car hard.
     
  14. Sirguydo

    Sirguydo Fastest milkman in the West Paid Member

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    Just got a litre of ate super blue from eurocarparts for 8.30 over the counter:thumbup: inc vat:thumbup:
     
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  15. Rayhoop Paid Member Paid Member

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    Hi guys, hate to put the cat among the pigeons, but I've been doing some digging around and would like your opinion...

    Eddie, awesome write up. Im tempted to put ate super blue in before bedford. But the "word on the net" about the mk5 liking thin brake fluid else the abs keels over got me thinking.

    Word on the net is usually unqualified so thought I'd see what I could find.

    I found this write up on brake fluid viscosity/performance and the table looked interesting.


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    Taken from the link https://www.google.co.uk/url?sa=t&s...PfshjpisFTD4b9VSQ&sig2=gcVaJsNiJAHVRucxm0v08Q

    I'm not sure which vw standard equates to the spec my mk5 needs, but if the boiling point info is correct then they don't perform too badly.

    My main thing though... Viscosity. So the rating at -40c us really low on the vw spec fluids... But realistically who is driving around at -40c in the UK... The interesting thing is at 100c, the viscosity is pretty on par with the fluids in Eddies write up... Which I would have thought would be more relevant?

    So if vw standard fluid is happy to run at 'normal' (1500mm2/s) viscosity at the higher operating temps... Do you think I need to worry about how thin (700mm2/s) it is at -40c?

    And at the same time. Is it worth a modern vag owner risking upsetting the teeves abs unit with out of spec fluid for what looks like not too much of a boiling point gain?
     
    Last edited: Mar 12, 2015
  16. Rayhoop Paid Member Paid Member

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    I've just realised ate do a low viscosity fluid which matches the vw spec. It's boiling points are not as high as 200/blue but are not too bad

    What I can't find are viscosity figures for 200/blue @100c to compare to the oem spec stuff...
     
  17. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    The Teeves system is also fitted to MK3 cars as my old Ankor in the picture.
    The 1300 centistokes mentioned for ATE Super Blue ( and by default TYP 200) would relate to cold flow in say a climate like Finland.
    As you put heat into the fluid from braking, the viscosity would drop to < 2 centistokes.
    ATE Super Blue was replaced by TYP 200, that does not have the blue colour. Same properties.
    Not sure what is the root cause for concern.
     

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