<VV> dot 3,5

[Bill Elliott]

That can be a difficult dilemma and one which I have faced myself. It's 
extremely important to ask the previous owner what brake fluid they used.

DOT 3, DOT 4, synthetic DOT 3 and 4, and  DOT 5.1 (also known as 
"racing" fluid) are all "glycol based", are fully compatible, and can be 
mixed with each other. The original spec was DOT3; the later fluids are 
later evolutions of that original fluid, each improving on the 
specifications (less hydroscopic, higher wet and dry boiling points, 
etc). Any of these can be used in a Corvair containing any of the others 
without worry. No reason not to use one of the "more evolved' fluids as 
the price differential is minimal.

DOT 5 is a completely different fluid and is not compatible with any of 
the above.  Inadvertently adding a silicone based fluid to a glycol will 
cause an adverse reaction.  It is also tinted blue/purple to help 
differentiate it from the other fluid types (which are generally 
clear/yellow)... but complicating things are the tendancy for the DOT 
5.1 manufacturers to also tint their fluids.

So if the car has clear/yellow fluid, you very likely have a glycol 
based fluid. If the fluid is tinted, you likely have DOT 5, but more 
investigation is in order to make sure you don't have one of the tinted 
DOT 5.1's. I've actually resorted to "feel" and "smell"... the glycol 
stuff feels and smells different from the DOT 5... it's a subjective 
call... I've also done some "test mixing" to see what happens to 
validate my choice before pouring...

Bill

cfm wrote:

>Some of the messages lately are about brakes and brake fluid.
>Hypothetically, if you just bought a car, or have owned one for a while and find yourself determining what kind of brake fluid to add to your system (if required), how is one to know which fluid to use?
>Do you default to DOT3?
>Can you mix 3 and 5?
>Can one inadvertently add a silicone based fluid to a non silicon system and get an adverse reaction?
>What type was OEM from Chevrolet at the factory?
>cfm
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