Screwed up on brake fluid. Used dot 3 but calls for dot 4. Need Help!

[vicgtr]

I topped up my brake fluid with dot 3 by mistake, it calls for dot 4. Is that REALLY bad, or just replace it when I get a chance?


Thx for your time
VIC

[vicgtr]

Can anybody help me?

[Blackice]

I am no BMW fluid guru, but why would you not just change it out ?

I did google it for you and here is the best answer I got. This from roadfly.

"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 "

[vicgtr]

Holy crap, thx for finding all that info for me. I am going to change it, I was just wondering if it needed to be done right away our can wait a week or two. Getting new rims and need oil change soon, will do it then.

Thx again for the info, it was very helpful.

[execuk]

no problem mixing dot 3 and 4
the only no-no is dot-5 and any other, as it is synthetic