Brake fluid 101 - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 39 (permalink) Old 05-23-2019, 07:53 AM
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Originally Posted by aenlle View Post
Bosch ESI6-32N Brake Fluid (Direct Replacement for DOT 3, DOT 4, and DOT 5.1) Just noticed this product for sale on Amazon. Has anyone have any experience with this product; seems to have good feedback on Amazon users. Longer duration and higher temp capability. Does it do OK with seals in our older Alfas? Here is a link.
That will be fine. It's a glycol fluid and meets Alfa specs. DOT 3, 4, and 5.1 are all glycol based and are compatible with each other.

DOT 5 is silicone, can't be mixed with the others, and is IMO a really bad idea for a street car.

People get confused because they think DOT 5 and DOT 5.1 are both silicone, and they aren't. Real naming screw-up there.


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post #32 of 39 (permalink) Old 05-23-2019, 08:39 AM
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Originally Posted by divotandtralee View Post
Can't see why it won't work or why it is better or worse than any other (unless you are on the race track) .. BEWARE DOT 5.1 is a GLYCOL based just like 3 and 4.. IT IS NOT COMPATIBLE WITH DOT 5.. the decimal point ONE matters

LMA is good and ATE is good and Prestone is good and Carquest is good...and on and on.. They all meet DOT standards and some have slightly higher boiling points or are more or less hygroscopic which allows them to be in service longer than some of the generics.. If you flush your system ever 12 to 24 months they all perform well. If you stretch it to 3-4 years ATE is good ( now only available on shelves as GOLD-- a DOT dictat) ( service periods are MY rule of thumb based on nothing scientific or what the container or mfr says)

I found this on the net...

DOT3 brake fluid is the "conventional" brake fluid used in most vehicles.
DOT3 fluid is inexpensive, and available at most gas stations, department stores, and any auto parts store.
DOT3 fluid eats paint!
DOT3 fluid absorbs water very readily. (This is often referred to as being hydroscopic.) As such, once a
container of DOT3 has been opened, it should not be stored for periods much longer than a week before use.
Since DOT3 fluid absorbs water, any moisture absorbed by the fluid can encourage corrosion in the brake lines
and cylinders.
DOT4 brake fluid is the brake fluid suggested for use in some late model cars.
DOT4 fluid is available at most auto parts stores, and at some (but not all) gas stations or department stores.
DOT4 fluid does not absorb water as readily as DOT3 fluid.
DOT4 fluid has a higher boiling point than DOT3 fluid, making it more suitable for high performance applications
where the brake systems are expected to get hot.
DOT4 fluid eats paint! Small leaks around the master cylinder will eventually dissolve away the paint on your
bodywork in the general vicinity of the leak, and then give rust a chance to attack the body of your car!
DOT4 fluid is generally about 50% more expensive than DOT3 fluid.
Since DOT4 fluid still absorbs some water, any moisture absorbed by the fluid can encourage corrosion in the
brake lines and cylinders.
DOT5 brake fluid is also known as "silicone" brake fluid.
DOT5 doesn't eat paint.
DOT5 does not absorb water and may be useful where water absorption is a problem.
DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.)
DOT5 does NOT mix with DOT3, DOT4 or DOT5.1. Most reported problems with DOT5 are probably due to some
degree of mixing with other fluid types. The best way to convert to DOT5 is to totally rebuild the hydraulic
Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5
formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent
Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can
cause localized corrosion in the hydraulics.
Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form
large bubbles over time. It may be necessary to do a series of bleeds.
DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4.
DOT5 is about twice as expensive as DOT4 fluid. It is also difficult to find, generally only available at selected
auto parts stores.
DOT5.1 is a relatively new brake fluid that is causing no end of confusion amongst mechanics. The DOT could avoid a
lot of confusion by giving this new fluid a different designation. The 5.1 designation could lead one to believe that it's a
modification of silicone-based DOT 5 brake fluid. Calling it 4.1 or 6 might have been more appropriate since it's a
glycol-based fluid like the DOT 3 and 4 types, not silicone-based like DOT 5 fluid.
As far as the basic behavior of 5.1 fluids, they are much like "high performance" DOT4 fluids, rather than traditional
DOT5 brake fluids.
DOT5.1 provides superior performance over the other brake fluids discussed here. It has a higher boiling point,
either dry or wet, than DOT 3 or 4. In fact, its dry boiling point (about 275 degrees C) is almost as high as racing
fluid (about 300 degrees C) and 5.1's wet boiling point (about 175 to 200 degrees C) is naturally much higher
than racing's (about 145 C).
DOT5.1 is said to be compatible with all rubber formulations.
DOT5.1 fluids (and Spectro's Supreme DOT4) are non-silicone fluids and will absorb water.
DOT5.1 fluids, like DOT3 & DOT4 will eat paint.
DOT 5.1 fluids are difficult to find for sale, typically at very few auto parts stores, mostly limited to "speed shops."
DOT 5.1 will be more expensive than DOT3 or DOT4, and more difficult to find.
All good points except DOT 3 absorbs moisture less readily than DOT 4. As the boiling point of brake fluid increases its absorbtion of moisture also increases. Cars used infrequently benefit from DOT 3 as the brake fluid remains dry longer than DOT 4 fluid and the higher boiling point of DOT likely isn't needed unless the car is raced.
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post #33 of 39 (permalink) Old 05-23-2019, 08:49 AM
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Rubber parts, including hoses; but I have never replaced the steel lines for DOT 5 conversion .. one of my cars with DOT 5 for 30 years.
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post #34 of 39 (permalink) Old 05-23-2019, 09:51 AM
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When I had all my brake components restored by White Post, about 2 years ago, they included a notice in the accompanying paperwork stating that use of silicone brake fluid would void the warranty.


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post #35 of 39 (permalink) Old 05-23-2019, 09:54 AM
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Good information.

One other slightly confusing thing is that the labels on cans of DOT 3, & DOT 4 brake fluid (and likely DOT 5.1, too) may say 'Synthetic'. I assume that is just marketing. But it seems like it could be confusing to someone trying to avoid silicone brake fluid...
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post #36 of 39 (permalink) Old 05-23-2019, 10:35 AM
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Originally Posted by ghnl View Post
Good information.

One other slightly confusing thing is that the labels on cans of DOT 3, & DOT 4 brake fluid (and likely DOT 5.1, too) may say 'Synthetic'. I assume that is just marketing. But it seems like it could be confusing to someone trying to avoid silicone brake fluid...
Yeah, all brake fluid is synthetic. As you suggest, it's just marketing.
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post #37 of 39 (permalink) Old 05-23-2019, 12:07 PM
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Silicone brake fluid

I suppose I should weigh in here, I'm a total convert to silicone fluid, we've been running it in cars for 30+ years now. I've successfully switched our entire classic collection over to it, except the vintage cable brake jobs

Full restorations with new hard lines are straightforward, the retro-fits are a little more complex, you need to flush the hard lines completely. Obviously when I do this all the wheel cylinders and master cylinder are off the car, so just the hard lines remain. I use a length of clear plastic tube over the bubble flares and pump neat Methylated Spirits (Meths - that purple stuff you had in the Bunson burners in the science lab way back at school).

Several successive flushes using a large syringe to pump the meths through the various hard lines works for me. Once done, I use compressed air to dry the lines. Leave open overnight. Then re-install the freshly rebuilt cylinders and couple the whole system back together. I then fill the reservoir with Bel Ray DOT 5 fluid. This is the brand my local motorcycle Speedyquip shop stocks. 1 small bottle will completely fill a Giulietta system and a second bottle facilitates the bleeding process. A vacuum pump does a fantastic job of sucking 90% of the entrapped air up from the MC & surrounding lines. The remainder I pump out via the bleed nipples at the wheels.

On that subject, pump the pedal.... s_l_o_w_l_y --> silicone aerates for nothing and an enthusiastic jockey on the pedal will see you leaving it overnight to let the bubbles dissipate. The first few squirts out the bleeder will probably contain a few purple spots - this is the dye in the purple Meths and will not harm anything. A bit occasionally stays behind when you blow the lines dry. 2 Pumps and its all out. I normally start with the wheel closest to the MC and work out from there.

Sprints, Spiders, the Ti, '68 Nissan Silvia Coupe, Dad's '30 Triumph Super Seven Tourer with original Lockheed hydraulic brakes all run on silicone DOT 5 Bel-Ray brand (imported from the USA)

I'm fastidious when cleaning & assembling brakes, several old ice cream tubs partially filled with meths, wash, rinse 1, rinse 2 & rinse 3 before assembling the wheel or master cylinders. Every part goes through the process, washers, seals the lot. On the subject of sealing washers, I always clean & anneal the copper washers, then clean them again & they also go through the wash rinse repeat process.

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post #38 of 39 (permalink) Old 05-23-2019, 01:44 PM
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I use DOT 4 brake fluid in all of my cars. I have DOT 5 brake fluid and would use it if I still raced my cars.
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post #39 of 39 (permalink) Old 05-24-2019, 05:52 AM
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Keep in mind that the "DOT" designation is just a minimum standard and not necessarily the spec of the fluid itself. For example, DOT 4 fluid is listed as a dry boiling point of 446*F, but Motul RBF 660 has a dry boiling point of over 600*F despite being listed as "DOT 4"

In general, standard cheap DOT 3 brake fluid is just fine as long as your car does not see extensive track or mountain use. For mountain use, a street-oriented DOT 4 is a good idea. For track use, fresh high performance fluid like Castrol SRF or Motul 600/660 is a good idea. I run Motul 600 in my daily driver, but I also flush quite often as it is tracked from time to time. The spider gets 600 as well, as it doesn't really need the boiling protection of 660. Castrol SRF is probably the best of both worlds in terms of track/street- it has a very high wet boiling point- but it is also very expensive at ~$70 a liter.

Last edited by nealric; 05-24-2019 at 05:56 AM.
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