Last Updated: 09/27/96

Brake Fluid Boiling Points

From: Kenneth Sax
The higher the boiling point, the better the protection against the brake system boiling and losing effectiveness. (Remember back to your chemistry class here. When a fluid boils, air bubbles form in the liquid. In a hydraulic system, the fluid acts like a metal bar that can push against your brake pistons. However, when air bubbles form in the brake fluid, the "metal bar" becomes very flexible, because air is much more compressible than the brake fluid. The result is a spongy feeling in your brakes because there is now a cushion of air in your brake lines that you are compressing before it pushes upon the brake fluid. Ed.)

Brake fluid is hygroscopic, which means that it likes to absorb water. When brake fluid is put into the system (from an unopened container), it is dry, meaning that there is no water in the brake fluid. At this time, its boiling point is at its highest - the "dry boiling point". Over time, the brake fluid will absorb moisture from the air, which lowers its boiling point, until it reaches the point when it has absorbed all the moisture it can. At this time, its boiling point is at its lowest - the "wet boiling point". Both boiling points are important in evaluating the protection that a brake fluid gives you.

Brake Fluids

Arranged by DRY boiling point: 
DRY: 401F -- WET: 284F --- DOT3 
DRY: 446F -- WET: 311F --- DOT4 
DRY: 502F -- WET: 343F --- Valvoline SynPower 
DRY: 509F -- WET: 365F --- Motul 5.1 
DRY: 527F -- WET: 302F --- AP Racing 551 
DRY: 536F -- WET: 392F --- ATE Superblue/TYP200 
DRY: 590F -- WET: 410F --- AP Racing 600 
DRY: 590F -- WET: 518F --- Castrol SRF 
DRY: 593F -- WET: 420F --- Motul RBF600 
DRY: 610F -- WET: 421F --- Neo-Synthetic Super DOT 610 

Arranged by WET boiling point: 
DRY: 401F -- WET: 284F --- DOT3 
DRY: 527F -- WET: 302F --- AP Racing 551 
DRY: 446F -- WET: 311F --- DOT4 
DRY: 502F -- WET: 343F --- Valvoline SynPower 
DRY: 509F -- WET: 365F --- Motul 5.1 
DRY: 536F -- WET: 392F --- ATE Superblue/TYP200 
DRY: 590F -- WET: 410F --- AP Racing 600 
DRY: 593F -- WET: 420F --- Motul RBF600 
DRY: 610F -- WET: 421F --- Neo-Synthetic Super DOT 610 
DRY: 590F -- WET: 518F --- Castrol SRF



Z.Speed Stainless Steel Brake Lines

[See review of this product on this site. -Ed.]
The benefit behind stainless steel brake lines is they don't expand as much
as the rubber ones. It eliminates the sponginess of the brake pedal because the
lines are braided steel vs rubber. They have no effect on cooling brake fluid.


Lucas Girling DOT 5.1 Brake Fluid

[See review of this product on this site. -Ed.]
Right now I would recommend Lucas Girling's DOT 5.1 brake fluid. It's a
synthetic fluid that is not silicon based and will work with all ABS and non-ABS
systems. It is yellow so it will be easily distinguishable when you bleed your
brakes. It boils around 276 degrees C. You can get it at Brake Warehouse for
$18.50 per liter. You need a little less than a liter to bleed the Integra's
brake system.
Motul also makes a good synthetic brake fluid which is DOT 3. It's available
at DC Sports in Ca. They sell it at $12.50 per liter. It boils at 300 degrees C.
Motul also makes a DOT 5 silicon brake fluid which is also available at DC
Sports for $7.50 per half liter. 
From: Kenneth Sax 
I'm using Motul 600 brake fluid
in my GS-R. It's a DOT 4 fluid rated at 585 degrees F dry, 421 wet, which is
more than any other that I've heard of. You can get it from Stillen Brakes at
714-755-6688. 
From: Walter Tani 
Tom Pultz mentioned some good
points about DOT 3, 4, and 5 fluids... he also mentioned that DOT 5 is SILICONE
based, which means you can't mix it with DOT 3 or DOT 4 fluids; it reacts
chemically and forms a precipitate. If you want to use DOT 5, you have to
disassemble the whole system and flush it thoroughly. Ditto if you are running
DOT 5 and want to change back to 4 or 3. You can mix 3 and 4 with no problems,
but i wouldn't. 3 will absorb water, as already noted; 4 doesn't so much, but
needs to be changed more often but for most performance oriented people is
probably the best compromise. DOT 5 is a bitch to work with, and very expensive;
i tried it awhile ago and although it prevents boiling and loss of braking power
from loss of pedal height because of the improved boiling pt, it is much
spongier initially, difficult to work with. 
The Ford HD fluids are great, a lot of racers use this because it is
manufactured by (I think)... Lotus? and is very expensive when sold by them;
Ford buys (or used to) a lot of it and slaps their name on it and resells it
much cheaper than Lotus does and the racers love it. I haven't tried it, the GT
LMA seems to work fine for me, but the reports I've read about the HD all agree
it is good stuff.