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  1. #1
    Eurodavid
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    Can someone comment about Dot 3 vs Dot 4

    Ok, I've been using Dot 4 brake fluid in my bmw when I do flushes, but I was a bit taken back yesterday when my BMW indie told me that you can use either dot 3 or dot 4 in the system, and you can even mix them. Minds you, this guy is one of the largest independent bmw dealers in Belgium, he races BMWs in Europe (mostly Belgium, Holland, France and Germany) and has won multiple times over the years, so I generally take what he says as pretty much true.

    I told him i thought the general rule of thumb was that you could use dot 4 in a dot 3 recommended system, but never the other way around. He said that is a load of myth & bullcrap, and that the only difference is the an additive put into dot 4 fluids to raise the boiling point a bit higher, plus there are some "super" dot 4s with a few more additives for better resistance in the battle with water. Otherwise, he said, dot 3 and dot 4 is essentially the same and can be used in any bmw, old or new, with equal effects and safety. He said the reason dot 4 is recommended by BMW (and all car manufacturers in Europe) is for two reasons: 1) most all European manufacturers settled on Dot 4 long ago to differentiate themselves from the USA & their use of Dot 3, and 2) to allow them to charge more for the fluid when selling it (this is true, as comparing Dot 3's price in dollars to Dot 4 from euros to dollars, dot 4 is 3-4 times more expensive over here).

    I was abit taken aback by this, so I came home and read on the internet to prove him wrong about Dot 3 vs Dot 4, and found this 2003 article:

    "Battle of the DOTs
    DOT 3-4 Verses DOT 5. Which brake fluid should I use?

    From Oak Okleshen #35 "With regards to the DOT 3-4 verses DOT 5 brake fluid controversy, here is an article sent to me by Mr. Steve Wall. It is one of the most professional treatments I have seen on the subject".

    [I had to condense this article from 6 pages to 1 due to space limitations -ed]

    Brake Fluid Facts
    by Steve Wall

    As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:

    1. Fluid compatibility with the brake system rubber, plastic and metal components.
    2. Water absorption and corrosion.
    3. Fluid boiling point and other physical characteristics.
    4. Brake system contamination and sludging.

    Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.

    First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry.
    Fluid Compatibility

    Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases.
    Water absorption and corrosion

    The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.
    Fluid boiling point

    DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes.

    DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.

    With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.
    Brake system contamination

    The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4.

    If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.
    New developments

    Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

    Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage."


    Well, it seems (following the logic of the article) Dot 3 or Dot 4 is identical, and, for instance, the argument about dot 3 eating rubber seals is basically just bullcrap and an owner created wives-tale sort of thing that has no basis in fact.

    Anyone agree or disagree? Comments? FYI: I stopped, this morning, by our military base DIY garage, talked to the 2 guys who work there, and they told me there are more than a few guys over here who run Dot 3 brake fluid in the BMWs, because it is so incredibly cheap when we buy it for them at the US military base exchanges, and have done so for ears with no problems

    Eurodavid


  2. #2
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    Re: Can someone comment about Dot 3 vs Dot 4

    DOT 3,4 and 5.1 are the same chemistry and are "compatible". Temperature and viscosity specs vary greatly. Use only DOT4 or better (ie. 5.1 is OK too) in a BMW particularly over in Yurrip where braking can be more extreme than in NA.

    DOT3 would be compatible with the materials, but not up to the task of stopping an E39 on the autobahn. I've also generally found that DOT3s may have very good dry boiling points, but wet boiling point is always superior on DOT4 fluids. Wet points are more important on the street where, if you're lucky, fluid is flushed annually, not "per event" or 3 times on a race weekend.

    DOT5 is silicone based on strictly not compatible with 3,4 or 5.1. It should pretty much never be used unless specifically called for. Water doesn't dissolve in DOT5 and collects into little bubbles or pockets of water in the system which will promote corrosion anywhere they happen to stop. In 3,4,5.1 water dissolves in the fluid and lowers the boiling points but at least it is "in suspension".


  3. #3
    Eurodavid
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    Re: Can someone comment about Dot 3 vs Dot 4

    Craig,

    Here's a link from a modertor on a vette forum:


    stops from 150mph to 0

    After researching for an hour or more reading on the Internet, the Dot 3 vs Dot 4 distinction ranks right up there with BMW "lifetime transmission" fluid.

    Do you know how rare it is to be at speeds above 150mph, let alone even stops from, say, 130mph or 140mph. I've driven on the autobahns for nearly 18 years now. The answer is: never.

    Only on tracking (track racing) do you see speeds like that, on here's the thing, "constant" braking> If you are braking from that kind of speed on the autobahns, two things are true: you're either close to death, or 2) you're already there.

    I'm not trying to knock using only Dot 4, but I use to think there was a massive difference between Dot 3 and Dot 4, that afffected every day street driving, or even autobahn driving.

    It just isn't true, especially for all of us on this board as we constantly (at a min) bleed/flush our brakes once a year, or at worst, once every two years.

    Eurodavid

  4. #4
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    Re: Can someone comment about Dot 3 vs Dot 4

    Not sure that I'd relate everything from a vette to an E39 - the braking system on the vette has much higher heat capacity than the single piston, floating caliper systems on the E39s. Not to mention different weight distribution under braking, different F/R brake bias, etc...

    There's a derivative of DOT4 with lower viscosity as well, which I remember hearing was developed for the X5s or something like that with all the electronic traction control all-wheel drive stuff they were doing. Viscosity while maintaining high boiling point is another factor to take into account.

    I don't see a big price difference, and DOT4 generally has higher temps than DOT3 across the board without a huge hygroscopic downside. While interesting, I personally feel it's a bit of a moot discussion - get the factory-spec DOT4 and move on. Analyzing the potential pros/cons of a higher spec fluid like DOT5.1, which does cost more - sometimes a lot more, may involve more analysis and critical thinking.
    While many DOT3s have the specs to work in E39s, the DOT3 minimum specs gave the engineers pause so DOT4 minimum specs were adopted. If you look around, you'll notice that even within the classes, boiling points are all over the map. What the specs don't say is the degree of hygroscopic behaviour, and how much water must be absorbed to reach saturation etc...etc... Highest boiling point is not the only factor to shop on.

    Other than theoretical discussion, I'm not sure why anyone would want to use a lower-spec fluid. It's not quite the same as the typical debate on lifetime lubricants. It's more like BMW specing a change interval and someone arguing to decrease that to lifetime, not the other way around. (BMW does spec a 100k interval now instead of lifetime, BTW)


  5. #5
    Eurodavid
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    Re: Can someone comment about Dot 3 vs Dot 4

    Craig,

    I am not trying to argue, what I am trying to do is bring things to light.

    You still miss the point: BMW engineers did not suddenly go "oh, Dot 3 miss our benchmarks way too much......blah, blah, blah" Do you understand that there is not ONE European auto manufacturer that uses Dot # fluid, and the reason is because the US auto manufacturers mostly use it (and have used it) in every vehicle they have made over the last few decades.

    There is no where on this Earth, outside of track racing, that an evident difference between Dot 3 versus Dot 4 will ever express itself or be made evidently. Nowhere. It is all in the imagination of the buyer, if they so choose to think that way. But it is imagination, not fact. Take a few hours (if you have them available), and read through the studies done on Dot 3 versus Dot 4, and the even more laughable Dot 5.1 specs (which are useful for vehicles stopping from 240mph+). If you ntice, the 150mph stopping figure quoted in that vette link I provided is the standard used in every other vehicle manufacturer brake system. Thus, no, it is not that vette and BMW braking system (or any other) are that vastly different.

    BMW engineers didn't do anything other than they normally do: they went with what all their peers inside Germany have done, which have publicly before said we absolutely WILL do it different than what US manufacturers have done.

    This evidence is made loud and clear by what all the Japanese manufacturers did in response. Check it out, it is very interesting to read. Also, maybe in Canada (or the US) there is no price difference, but in Yurrip, there is a whale of a difference between buying Dot 3 (let alone even finding it) versus the ubiquitous Dot 4.


    I am only trying to discuss this stuff for informational purposes, to demystify a lot of auto manufacturers tell you and would have you believe. I've met over 8 BMW engineers now (through auto clubs), and believe me, when you hear them talk (and see what they do to their BMWs), you would have a whole another opinion than what you might be holding about them. "Reverse engineering"s a term to them that is very dear, especially, lately, from the Asian side of things.

    Eurodavid

    PS This discussion is very similar to people who believe the BMW line about only 5w-30 oil is the best for their BMWs. I have not met one BMW owner here in Europe at the clubs I go to, whether they own a brand spanking new BMW or a very old one, that runs 5w-30. And this is true for even the guys from the extreme, artic-like cold north of the country. They all run either 15w-50 or 20w-50, because, as I have tried to mention on here before, all BMW engines, to this day, are designed with that weight in mind. They are forced to go the 5w-30 rote not because of tight tolerances, of new engine design, or anything else, but because of EPA and also European highway mileage requirements---all the while fully knowing that that 5w-30 engine oil isn't what BMW engines are designed around in mindset and in prototype testing. This isn't just some made up fairy tale over here, it is based in fact, especially if sit down and talk to well known GErman BMW people and BMW dealers.


  6. #6
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    Perhaps the simple thing to do is find a brand...

    you like, and stick with it. I've used Castrol LMA for MANY years.

    Ford USA has a highly-acclaimed DOT-3 brake fluid that is specified for severe service; e.g., trucks and RV chassis.
    Ed in San Jose. BMW CCA member since 1980 (Nr. 62319). Golden Gate Chapter

    '97 540i 6 speed. Build Date 3/97. Aspensilber over Aubergine leather.

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