# Dot3 vs. Dot4



## NoCYet (Feb 10, 2001)

Are there any visual differences between Dot3 and Dot4 brake fluid? I bought a '92 Corrado which had major brake work done, and I want to make sure the right fluid was used, since most cars use Dot3. Also what kinds of nasty things will happen if the 2 are mixed?
thx.


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## scolen2 (Jan 16, 2002)

*Re: Dot3 vs. Dot4 (NoCYet)*

Flush it and put in 5.1 and have no worries! ;-)


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## G60Johnster (Jan 10, 2002)

*Re: Dot3 vs. Dot4 (NoCYet)*

DOT3 and DOT 4 are basically the same type of fluid (as opposed to DOT 5, which I'll get to in a sec)
You can mix the two, but it'd kinda be like mixing motor oil brands - yeah, it'll work fine, but if you do it forever there might be some 'additive package' conflicts. Nothing major I'd guess, should be safe mixing 3 and 4.
The difference is that the DOT3 standard has a lower temperature rating than the DOT 4- meanign the DOT4 can withstand higher temps. I think this is why most brake systems are labeled DOT4 on them, but most books say 'use DOT 3 or 4'. Liability thing. If dot3 were unsafe, then some safety nazi would appeal untill it dissapeared on store shelves, so Its by no means BAD...
3 and 4 I guess are kinda like motor oil, yeah, you can spend more, and feel better, but dont be surprised if someone buying the cheaper stuff has the same effects (I still buy dot4 and expensive oil though








DOT is mineral oil based fluid, used in Bentleys mostly. do not even THINK about putting dot 5 in your VW (eats seals for breakfast).
I've never heard of "5.1"
Peace -John


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## NoCYet (Feb 10, 2001)

*Re: Dot3 vs. Dot4 (G60Johnster)*

thx for the reply, I thought that dot 5 was silicone based though.


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## Knestis (Jun 22, 2001)

*Re: Dot3 vs. Dot4 (NoCYet)*

The trade off cost for higher temperature tolerance (when the fluid is NEW) is that DOT4 fluids tend to absorb moisture from the atmosphere more quickly than DOT3 - thereby lowering the boiling point. If you are racing and bleeding your brakes regularly, this isn't a problem but, for street applications, use what your book recommends (probably -3). In reality, you will NEVER get the brakes hot enough on the street to ever know the difference.
Kirk


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## CRL87VW16V (Jan 20, 2002)

*Re: Dot3 vs. Dot4 (Knestis)*

). In reality, you will NEVER get the brakes hot enough on the street to ever know the difference.............................
I have a A2 golf that I had the brakes so hot ripping around with some buds that when I finally came to a stop, I let two big clouds roll out from my wheel wells















smoked so bad I thought my car was on fire !!! nevre get the brakes hot enough 
HA!!!!!!!!!!!!!!!!!!


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## spitpilot (Feb 14, 2000)

*Re: Dot3 vs. Dot4 (CRL87VW16V)*

Letting fluid go too long between flushes will do more to degrade your braking performance than putting in DOT 3 fluid! I've used Castrol GT LMA (low moisture absorbtion) fluid with excellent results for years and years. "Exceeds DOT 3& 4 requirements, Min Boiling Point 446 deg. F, Min Wet Boiling Point 311 degree F." Pep Boyz sells for $5 or so a quart. Just change the stuff every other year! Never a rusted or gunked up caliper or wheel cylinder!


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## M this 1! (May 17, 2000)

*Re: Dot3 vs. Dot4 (spitpilot)*

you can't mix the others with dot5, it'll corrode the lines. 5.1 was supposed to o.k. to use for a wider range of uses but i've not used it. and i'm sure what he meant about street use was the fact that you may have smoked the hell out of your pads, you still probably didn't get the fluid into a boiling situation. if you're going that hard you just needed a better pad. in your situation you'll hit serious fade WAY before sending enough heat thru the system to over heat the fluid.


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