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DOt 3 contains alcohol. So did prewar anti freeze.
What keeps the alcohol in DOT3 and anti freeze from turning to vinegar????

Vinegar is an acid. Acid corrodes metals.

THe reason i ask is that on rare occasions i've had wine turn to vinegar. Never known of whiskey turn to vinegar tho.

So why doesn't DOT3 and the old Ethyl alcohol anti freeze turn to vinegar too?????

The alcohol in brake fluid isn't a simple alcohol like ethyl or methyl. It's a very much different member of the class, extremely high boiling, pretty much unreactive.


Don't know enough about wine chemistry to comment.

Acetic acid (vinegar) forms in beer and wine as a result of bacterial metabolism. Essentially, it is caused by the breakdown of ethanol to liberate energy during glycolysis. When alcohol concentrations are high, the reaction does not progress completely to the formation of acetyl-COA for every molecule of ethanol, but stops at the formation of acetylaldehyde, which then gets quickly oxidized to acetic acid.

No bacteria, no vinegar.

More than you wanted to know?

I have seen Dot-3 brake fluid turn to Jello, crumbly Jello at that.

I'm not sure what the British use for brake fluid, but I saw the fluid in a Nash Metropolitin turn into gumballs. When fresh British fluid was added it turned liquid again. Very odd.

Randy--Castrol makes a brake fluid that is used in Rolls Royces, it is the only fluid you can use for many years of RR, they may still use it. I wonder if that is what you are reffering to?

The fluid in my old lines was tuned to a solid rusty mass. The corrosion was so bad I was never able to remove the lid from my old master cylinder. Not even an impact gun, torch heat or a breaker bar could budge it. So I ended up just buying a new replacement. Crazy.

I use DOT4 in the Caribbean and try to flush and change it every 2-3 years, it's always very clean when it flushes out. DOT4 is said to be compatible with DOT3 though I don't recommend mixing them. It offers a somewhat improved (higher) boiling point and is said to be a bit less hydroscopic (moisture absorbing).

Tom Wilcox: The bacteria - how could that have escaped me, of course!!

I just bought some DOT 4 to fill the Clipper with. Also they make DOT 5.1 which is similar in composition to DOT 3/4 (polyethylene glycol-based fluid), but with a much higher boiling point that is comparable to the boiling point of DOT 5 (Silicon). Put it's pretty pricey and typically used in racing applications.

You can drain a DOT 3 or 4 system and simply refill with DOT 5.1, unlike DOT 5.

Really the main difference between DOT 3, 4 and 5.1 is the a difference in the boiling points. All 3 are hygroscopic polyethylene glycol-based fluids.

Boiling point ranges

===Dry boiling point==Wet boiling point==Fluid Type
DOT 3---205?C (401?F)--140?C (284?F) polyethylene glycol
DOT 4---230?C (446?F)--155?C (311?F) polyethylene glycol
DOT 5---260?C (500?F)--180?C (356?F) silicon
DOT 5.1-270?C (518?F)--191?C (375?F) polyethylene glycol

Thanks Kev, I wasn't aware of DOT5.1.

I've known of several instances when 3.0 "boiled" in the wheel cylinders from heat caused by extremely heavy braking which of course results in loss of hydraulic pressure and causes temporary loss of brakes. After cooling down the braking action returns to normal. Some folks have mistakenly attributed this to master cylinder failure but of course it is not.

DOT4 is the currently recommended brake fluid for BMW.