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Brake fluid: Is Dot 4 ok? Opinions?

S

sothpaw

Guest
I was shopping for some brake fluid just now,
as I'm going to road race in 3 months and I'm concerned
about the fluid. Last time it boiled on me, and I lost all
braking ability in seconds.

Question: Although the 'vette owners manual calls for Dot3, can
I use Dot4? I got some Ford fluid, and the Wet boiling point
is 380 F or so for Dot 4. The Dot 4 can also said not to use it if the car calls for Dot 3(yikes). The Ford Dot3 fluid said Dry bp of
550 F, and that it exceeded the Dot3 min of 250F(or thereabouts).

What the heck is a dry bp? a wet one? I thought bp was the temp at which the liquid changed to gas at a given pressure.

Thanks!
 
Joined
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none right now :(
You should do fine with the Dot 3 fluid anyway, if you bleed the whole system... Any water that gets into the system drastically reduces the boiling temperature, and brake fluid absorbs water naturally... on top of that, brake systems are not completely sealed, there is water in the air so... after a few years your brake fluid starts to not work well... you could also check the newer brake fluids designed to work with dot3 and dot 4 specs... I think they also have a higher boiling temperature


Wet boiling point is much lower than dry boiling point....
Dot 3 is: Minimum dry boiling point :450 degrees
Minimum wet boiling point:284 degrees
these are the new numbers for dot3, there are others out there, but they are all close...

also, 3% water contamination in brake fluid = 25+% lower boiling point... it takes apprx. 12 months to reach 2%, 18 months to reach 3% on most cars.
 

WhalePirot

Well-known member
Joined
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1984 White Z-51/ZF6-40/Shinoda body
bp= boiling point

The DOT 4 fluid meets a higher standard than the DOT 3, with better high temperature characteristics and consequent less water absorption. The boiling point issue is a non-starter for me, as I've never gotten the fluid that hot.

Personally, I like Valvoline products and have a 'can' of their synthetic formula DOT3 & 4 in front of me. The boiling point exceeds 500F (by 2 degrees) and the wet is 343. It is compatible with DOT3 and claims to exceed DOT 4 specs.

I change my cars' brake fluid when it gets dark, flushing the system by sucking new, clean and dry fluid through each caliper, after removing as much old fluid from the reservior, replaced by new. I consider it cheap insurance, as the moisture therein corrodes the pistons and cylinders, causing uneven or inoperable brakes (clutch), requiring expensive component replacement. A Honda dealer told me, years ago, that in our dry climate, flushing was not necessary. I disagree, having replaced enough corroded brake parts. In wetter climes, 6-12 months may be routine intervals. This is one of those personal choice areas, like frequency of oil changes.

I like this DOT 4, being cheaper that the racing fluids with none of the sponginess of silicon fluid and more resistant to moisture build-up than the 'earlier' fluids.

:w
 
S

sothpaw

Guest
dot4 even when can says not to

So nobody sees a problem with using Dot 4,
even though the can says not to with a car requiring Dot3?
That's what I was shooting for.

--Yes, I'm definitely going to bleed the system. It's been almost
3 yrs. Every 6 months? I hope I'm not screwing things up, I've
never done it that often.
 
C

CDN88

Guest
Re: dot4 even when can says not to

sothpaw said:
So nobody sees a problem with using Dot 4,
even though the can says not to with a car requiring Dot3?
That's what I was shooting for.

--Yes, I'm definitely going to bleed the system. It's been almost
3 yrs. Every 6 months? I hope I'm not screwing things up, I've
never done it that often.

All I can tell you is that the '88 I'm driving says DOT 3 right on the master cylinder caps...
 
Joined
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1986 Bright Red Coupe
CDN88, it wouldn't surprise me that your Vette says DOT3 on the cap - I don't think they had DOT4 15 years ago.

Sothpaw, what's the stuff that Paul recommends? That's what is currently in my Vette.
[RICHR]
 
Joined
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I'm with WhalePirot, I use Valvoline sythetic Dot 3/4 in all of my cars. Higher boiling point, less moisture absorption, you can't go wrong.

- Eric :w
 
Joined
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none right now :(
I use the same stuff... pretty cheap too, I think a big bottle is only around $5, and it is enough to bleed the whole system.. I am pretty sure the C5 still calls for Dot 3 though, I would stay away from any fluid that specifically states not to use it on Dot 3 brake systems.
 
C

c4ever

Guest
I use Castrol Dot 3/4. Never a problem.

Carlo
 

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