Brake Fluid - Dot 3, 4 or 5 ??? |
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GranTorinoSport
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Posted: 05-January-2006 at 11:36AM |
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I was reading a Ford Muscle Magazine article, and they claimed to be using DOT 5 in a project car (Torino or Montego, can't remember). Provided you are doing a complete brake overhaul, to include lines and everything (or you are willing to flush the system), is it worth it? Everything I have read about DOT 5 is that the silicone is a good performer, but tempermental. I have even heard of people boiling the fluid on the stove to get the air out before putting it into their car. I'd like to use DOT 5 if it is really that great, but I am not boiling brake fluid on my stove! |
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Scott Eklund
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GranTorinoSport
Admin Group Admin of "The Org" Joined: 20-May-2003 Location: Seattle Status: Offline Points: 2287 |
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OK, I am slowly finding my own answer. I will post information here as I find it.
Here is one old posting on a board from 1999: Date: Fri, 12 Mar 1999 22:09:46 -0500 From: "Steve D'Gerolamo" <steved3idt> Subject: Brake Fluids Thanks to Dave Zeckhausen who is as obsessive about brakes as I am about tools. This is one of his well circulated postings: Lets look at what the DOT ratings mean. The table below shows the MINIMUM wet and dry boiling points for DOT 2, 3, 4, and 5 brake fluid in degrees fahrenheit: DOT 2 DOT 3 DOT 4 DOT 5 Dry Boiling point 374 401 446 500 Wet boiling point 284 311 356 The DOT 2 spec is for drum brakes and is obsolete. If you have any DOT 2 in your garage, throw it away! DOT 5 is for silicone brake fluid. Silicone brake fluid (DOT 5) should be avoided because it is not compatible with regular brake fluid, it is hard to pour without introducing bubbles and thus results in soft pedal feel, and moisture still gets into your system and will pool in low areas like your calipers and encourage rapid corrosion. STAY AWAY! That leaves DOT 3 and DOT 4 fluids. These fluids are compatible with each other and may be interchanged or mixed with no ill effects. Let's look at some popular brake fluids and their boiling points: Fluid DRY WET Castrol LMA DOT 3/4 446 311 Ford Heavy Duty DOT 3 550 290 ATE Super Blue Racing 536 392 ATE TYP 200 536 392 Motul Racing 600 585 421 Castrol SRF 590 518 Performance Friction 550 284 Castrol LMA is very good at rejecting moisture and may be kept in your brake system for a couple years. The LMA stands for "Low Moisture Absorption". This is the minimum quality stuff that I would use in my Impala. It comes in plastic containers which do not have a long shelf life. Don't buy lots of this stuff at a time because moisture can make its way through the plastic containers. Ford Heavy Duty DOT 3 is VERY inexpensive and is popular among racers because of its excellent dry boiling point. It absorbs moisture quickly, but the racers don't care since they change their fluid frequently. Comes in metal cans so it may be stored. I would not use this in my Impala for the street. ATE Super Blue Racing and ATE TYP 200 are the same brake fluid in two different colors (blue and amber, respectively). BMW recommends this brake fluid for their street cars because it, like Castrol LMA, absorbs moisture very slowly. The advantage over LMA is that ATE has a much better wet boiling point. You can put this stuff in your car and forget about it for a long time. An excellent choice for a weekend track car which also sees regular street duty. Comes in metal cans. This is what I use in all my street cars. Motul Racing 600 is a very exotic and expensive synthetic fluid with high wet and dry boiling points. I use this exclusively in my race cars. Too expensive for the street and requires frequent changing due to its hydroscopic nature. Sold in plastic bottles. Castrol SRF is a hyper-exotic and hyper-expensive brake fluid that is generally used by wealthy Porsche owners at track events. I've seen prices of $78 per liter for this stuff. It is not suitable for the street because it absorbs moisture quickly. Sold in metal cans. I can't afford this stuff! Performance Friction High Performance DOT 3 has a good dry boiling point but a crummy wet boiling point. It comes in metal cans which is good for shelf life and sells for $7.87 per 16 ounce container. If you are even considering this fluid, I would go with the cheaper Ford Heavy Duty DOT 3. In either case, change this fluid frequently due to the poor wet boiling point. |
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Scott Eklund
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GranTorinoSport
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Yet more information:
|
PROPERTY |
DOT 3 |
DOT 4 |
DOT 5 |
Dry BP (F)@ 0.0% H2O |
401 |
446 |
509 |
Wet BP (F)@ 3.7% H2O |
284 |
311 |
356 |
Chemical Composition |
Glycol Ether Based |
Glycol Ether /Borate Ester |
Silicone Based |
As a trailing note on the DOT ratings, if your car was designed for a particular type of fluid (especially prior to the development of DOT 4 fluids), you should make every attempt to stick with that fluid! For example, if your car was delivered with DOT 3 fluid, the internal components of the system (seals, brake hoses, and fittings for example) were specifically designed and tested for compatibility with DOT 3. Because DOT 4 fluids contain a different chemical composition, the system may not necessarily react in a positive fashion to the borate esters floating around in the mix.
In other cases, just the difference in viscosity of the two different fluids may cause the seals to wear at different rates. What starts as an annoying squeak might eventually become a torn seal or worse. The examples could go on and on, but the message here is this: it’s fine to upgrade from DOT 3 fluid A to DOT 3 fluid B, but you should think twice (maybe even three times) before switching from DOT 3 fluid A to DOT 4 fluid of any sort.
That said, when dealing with modern hydraulic braking systems a numerically higher DOT rating is typically considered to be compatible with a lower DOT rating (except for DOT 5, of course). Unfortunately, this same generality just isn’t true for most older hydraulic system materials.
While the performance enthusiast is most concerned about boiling points, the
government holds no less than fourteen properties of brake fluid in the highest
regard. Fail just one of the tests, and the product cannot be legally offered
for sale in the
1. Dry boiling point
2. Wet boiling point
3. Kinematic viscosity (how thick the fluid is, with lower generally considered
better for flow)
4. pH value (measure of acidity, with higher generally considered better for
corrosion resistance)
5. Chemical stability
6. Corrosion
7. Fluidity and appearance at low temperature
8. Evaporation
9. Water tolerance
10. Compatibility
11. Resistance to oxidation
12. Effects on rubber
13. Stroking properties (lubrication capability)
14. Fluid color
In order to detail each requirement, we would need to reproduce the entire FMVSS116 document here in its entirety. Since that would probably put 99% of all readers to sleep (the regulation is comprised of no less than twenty two pages of brake fluid minutiae), we’ll just provide this handy link:
Dig around enough and you can find it. If we gave away the direct link it would take away half of the fun of navigating a federal government department website…
Why the heck do we use brake fluids that absorb water in the first place?
Believe it or not, one of a brake fluid’s most vital characteristics is its ability to absorb water. Yes, you read that correctly – brake fluids absorb water by design and that is really a good thing.
What?
Whether we like it or not, water is everywhere and finds its way into everything. That’s just the nature of the beast. Even our brand-new sealed brake system will eventually absorb water given enough time.
The magic of diffusion allows moisture in the air to permeate microscopic pores in the rubber brake hoses, the nylon master cylinder reservoir, and the various rubber seals in the hydraulic system. Sadly, there is nothing we can do about it and if left unchecked the water would sit in our brake system and rot it away from the inside out.
Hence the need for brake fluid to absorb this unwanted house guest. Because brake fluid absorbs water into solution, the local concentration levels are typically low enough that corrosion is slowed dramatically. As an added benefit, when exposed to low temperatures, the solution state prevents the water from pooling and freezing on its own. While water in brake fluid will certainly increase the solution viscosity at low temperatures, this is much more desirable than having little chunks of ice plugging up the system!
So, the next time you are bleeding your brakes to remove the water-contaminated fluid, don’t curse at the automotive gods too loudly. After all, the fluid was only doing its job.
Historically, DOT 5-level performance (specifically boiling points and viscosity) could only be achieved with silicone-based fluids. However, modern compounding has created glycol ether-based fluids which now meet DOT 5 bogeys in these key areas. Consequently, the DOT 5.1 moniker was created to differentiate between these two very different chemistries which both meet DOT 5 performance requirements.
In so many words, DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements. Because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern. In some circles, they are even referred to as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids because they are more similar to a conventional DOT 4 fluid by chemistry than they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially comprised of Borate Esters.
While it may not be obvious, the big advantage of the DOT 5.1 fluids is that they contain all of the nifty water-absorbing characteristics of the DOT 3 and DOT 4 fluids while simultaneously providing for very high boiling points and relatively stable viscosity over a wide range of temperatures. The best of all worlds, you could say. The table below sums it up quite nicely.
PROPERTY |
DOT 4 |
DOT 5 |
DOT 5.1 |
Dry BP (F)@ 0.0% H2O |
446 |
509 |
509 |
Wet BP (F)@ 3.7% H2O |
311 |
356 |
356 |
Chemical Composition |
Glycol Ether / Borate Ester |
Silicone Based |
Glycol Ether / Borate Ester |
(As stated earlier, the table data above contains the minimum properties for a fluid to be called a certain type. For example there are many racing brake fluids with Dry BP performance at or above 590o F and Wet BP at or above 390o F.)
So, what is the downside of the DOT 5.1 fluids? Like most things in life, the good stuff isn’t cheap. DOT 5.1 fluids typically cost three to four times as much to manufacture as a conventional DOT 4 fluids. There’s always a catch…
On their own, silicone-based DOT 5 fluids are entirely different animals than DOT 3 and DOT 4 fluids. In addition to having characteristically higher dry and wet boiling points, they also tend to have much, much lower viscosities. In other words, they flow more easily relative to temperature.
One side effect of this chemistry is that there is more “room” for air to fit in-between the individual molecules of brake fluid than in DOT 3 or DOT 4 fluids. Note that we are not talking about big bubbles of air here which are visible to the naked eye, but rather microscopic amounts of air which are finely dispersed (entrained) in the brake fluid matrix.
Now, all fluids have a certain amount of compressibility to start with, but
adding even the smallest amount of air into the solution can dramatically
increase the amount of elasticity in the system. In the case of silicone-based
fluids, air is quite happy to take up residence between the brake fluid
molecules, and as a result the fluid compressibility goes down. This is felt at
your foot like stepping on a
Pressure bleeding on its own is not necessarily a bad thing, but there are several steps one must take to ensure that the bleed event will result in an air-free brake system.
When we talk about pressure bleeding, we are referring to the process in which we pour our brake fluid into a pressure vessel, hook up a pressure source, and run the now pressurized fluid directly into the master cylinder reservoir. One by one the caliper bleeder screws are opened to allow the pressurized fluid to flow through the system until all of the old fluid has been purged. Simple, right?
Well yes, but beware of imitations – not all pressure bleeders are created equal. The professional units (the type you can consider using) separate the pressurized brake fluid from the pressure source (air) using a flexible rubber diaphragm. In this fashion, the pressurized air is kept from forcing its way into the fluid. As we all know, air and fluid should be kept as far apart as possible.
This brings us to the imitations. There seem to be a rash of products available lately that claim to be pressure brake bleeders at a fraction of the cost of the professional units. Like most things that sound too good to be true, well, it’s exactly that.
Like the professional units, these imitations contain a pressure vessel into which new brake fluid is poured. However, in order to pressurize the fluid, an integral pump handle is cycled to build the pressure inside the vessel without any measures taken to separate the pressurized air from the fluid. For those of you who have ever bought a $19.95 do-it-yourself potted plant and bug sprayer from Home Depot you get the idea.
Of course, having pressurized air in contact with the brake fluid will certainly force the fluid through the system just as effectively as the high-zoot professional unit, but as an added bonus we are stuffing air into the brake fluid at the same time. Talk about an unwanted surprise!
While it may not be visible to the naked eye (air can actually entrain itself in the fluid as to be visually undetectable) it’s there right along with all of the nasty moisture trapped inside of it. This of course begs the question: if you are stuffing air and water contaminated fluid into your brake system, why even bother bleeding it in the first place?
Naturally there will be those who argue that the amount of air in question is not important enough to worry about, but think about this for a moment: nearly every automotive manufacturer stores their bulk brake fluid in large containers which are subjected to a constant VACUUM. Talk about an expensive process! If just storing your fluid under regular atmospheric conditions isn’t good enough to keep air and water out, just imagine what shoving 30psi worth of compressed air on top of it is doing.
The professional units can cost hundreds of dollars, and for good reason; unfortunately the cost keeps them beyond the reach of most of us normal folks. Your best bet is probably to get back in the driver’s seat and begin stroking the pedal with your foot again, but ultimately the choice is yours.
No magic here. However, be forewarned that if you are taking your car to the track there are NO fluids which allow you to run indefinitely without periodic bleeding. The best that a fluid can do for you is provide stable, consistent performance while lapping, but because all fluids will absorb water over time, all fluids must be bled at some point. It’s that simple.
That said, find the best DOT-compatible fluid that fits your budget and is readily available to you. If your fluid never boils on track, you’re done – there’s your “right” fluid. However, if fluid fade persists, you may have to bite the bullet and pay up the ladder for the next best thing. Speed costs money as the saying goes, and so does performance braking.
FOR A SIDE-BY-SIDE BRAKE FLUID COMPARISON OF BOILING POINTS:
Brake Fluid |
Dry Boiling Point |
Wet Boiling Point |
Suggested List Price |
AP SUPER 600 |
590°F |
410°F |
$18.00/16.9oz. . |
CASTROL SRF |
590°F |
518°F |
$69.99/33.8oz. |
NEO SUPER DOT 610 |
610°F |
421°F |
$15.00/12oz. |
MOTUL RACING 600 |
593°F |
420°F |
$15.00/16.9oz. |
MOTUL DOT 5.1 |
509°F |
365°F |
$6.50/16.9oz. |
ATE SUPER BLUE |
536°F |
392°F |
$11.99/33.8oz |
VALVOLINE SYNPOWER |
503°F |
343°F |
$4.97/16.9oz. |
ATE SL |
500°F |
329°F |
$7.95/16.9oz. |
CASTROL LMA |
450°F |
311°F |
$3.50/16.9oz. |
AP 551 |
528°F |
288°F |
$12.50/16.9oz. |
Hot damn, no one mentioned super tech brake fluid, which is what I usually use (walmart) (half sarcasm)
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