The information & links posted by Paulster2 offer excellent explanation of what the various types of brake fluid are.
There are a few grade :
The difference between them is a specificed standard regarding the boiling temperature, which rises as the DOT number rises, and amount of water absorption.
There are based on two ...
For everyone's edification, here are the dry/wet boiling point specifications for the different brake fluids:
Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5 260 °C (500 °F) 180 °C (356 °F)
DOT 5.1 260 °C (500 °F) 180 °C (356 °F)
The biggest advantage to DOT5 brake fluid is that it is hydrophobic meaning it doesn't like water. This is in contrast to DOT 3, 4, 5.1 which are hygroscopic which means it will absorb water even just out of the air. This is a huge advantage if storing the car for most of the year and only breaking it out a few times during the summer. If using any other ...
Check Brake Fluid on Wikipedia.
DOT 5 is not interchangeable or compatible with DOT 3, 4, and 5.1 fluids and can cause catastrophic system failure.
Dot 3, 4, and 5.1 are glycol ether based. They are compatible, but like motor oils, you should use the recommended or higher grade fluid.
Dot 4 and 5.1 also have borate ester to handle higher temperatures.
I found this description of synthetic based brake fluids. According to the page, all brake fluids are technically "synthetic" in that they are man made and do not contain a petroleum base.
"Synthetic" brake fluid, as we think of it, has a silicon base. Non-synthetic brake fluid (normal brake fluid) is glycol based. There are trade offs to each type. Silicon ...
You can absolutely use DOT4 in place of DOT3 brake fluid. The only thing you'll need to do is completely purge the system of the old DOT3 fluid to take advantage of the DOT4 features (higher boiling point both dry/wet). The only real difference between the two is how hot they can get before they boil. The DOT4 will not harm your DOT3 system in any way. Do ...
DOT 3, 4 AND 5.1 can be mixed. They are compatible. None of them are compatible with DOT 5 that's silicone-based.
I just bought some Motul DOT 5.1 and it says on the front label: "NON-SILICONE base DO NOT mix with DOT 5. DOT 3 and 4 are compatible."
The main difference between DOT 3, 4 and 5.1 are the boiling points, both wet and dry. The higher the ...
DOT 5 is silicone based and is no way compatible.
Dot 5.1 is sort of OK but not recommended to mix with 3 and 4.
To use Dot 5, you MUST replace all rubbers, seals and flex brake lines as well as flush steel lines.
How do I know ? I am running it in my muscle car.
Manufacturers have been labeling their DOT3 and DOT4 products as "synthetic" as many consumers associate this with higher performance or quality similar to motor oil. But ALL brake fluids can be called synthetic. You can mix any of them except for DOT5. Even DOT5.1 is OK since this also a glycol based fluid.
If you mix DOT3 and DOT4 fluids (or different ...
EDIT EDIT of my not being able to read:
From the 96 Civic owners manual: "use Genuine
Honda Brake Fluid or an equivalent
from a sealed container that is
marked DOT3 or DOT4 only. Brake
fluid marked DOT5 is not compatible
with your car's braking system...
the same DOT3 or DUT4 brake fluid
specified for the brake system [for the clutch]."
The Bosch Automotive Handbook confirms that mineral-oil-based fluids are not hygroscopic:
Mineral-oil fluids (ISO 7308)
The great advantage of mineral-oil-based fluids is the fact that they
are not hygroscopic, so the boiling point does not drop due to
It also makes clear that mineral-oil fluids are incompatible with systems designed ...
The only difference between the two is the boiling point of the fluid, with DOT4 having a higher range. You could use either and get away with it, but if the cap on the master cylinder states it should be DOT4, that's what I'd go with. Even if DOT3 is all that is required, DOT4 will add a little bit better boil resistance. The two different types can be ...
A couple of things here. First, when I find the brake reservoir low, I will look at my disk brakes to ensure the pads aren't shot (or nearly worn out). Usually, if worn enough, the fluid level will drop to a point where the brake light will come on as you described (most notably so if both back and front are worn out).
With that in mind, consider just ...
Dot 4 supercedes Dot 3.
If you put Dot 4 in, no problem. Basically, Dot 4 can go in and replace Dot 3, chances are you already have Dot 3 in anyway.
Wikipedia, Dot 4:
While a vehicle that uses DOT 3 may also use DOT 4 or 5.1
Note: Dot 5 is not compatible with either, it is a different chemical makeup based on silcon. Putting Dot 5 in a Dot 3/4 system ...