Brake Fluid Overview
Current DOT ratings for brake fluid is DOT 3, 4, 5 and DOT 5.1. DOT 5 is silicone based and all the others are glycol based. The DOT 5 silicone based brake fluid is not compatible with the any other brake fluids.
Brake fluids are made up of mainly to different type bases.
The DOT ratings
NOTE:The DOT 2 spec is for drum brakes and is obsolete. If you have any DOT 2 , do not use it. DOT 5 is a silicone brake fluid. Silicone brake fluid (DOT 5) should be avoided because it is not compatible with regular brake fluid.
DOT 3 and DOT 4 fluids are compatible with each other and may be interchanged or mixed with no ill effects.
The DOT specifications are based on the concept of wet and dry boiling points. The dry boiling point is applicable when fluid is fresh and the wet boiling point after the fluid has been exposed to moisture and has had the opportunity to adsorb water. The minimum values for the wet and dry boiling points are specified for each DOT level, and increase from 3 through 5.
Below are some popular brake fluid specs.
Why do we worry about the Wet Boiling point?
I normally use the ATE brake fluid and alternate between the Gold and the Blue.
The different colors make it easy to tell when you have completely flushed the old
fluid out. It normally runs around $10.00 a liter and I change it every other year.
Low Viscosity Brake Fluid
Recently I was getting ready to order some ATE brake fluid and noticed on their website they had a new brake fluid that was optimized for ABS braking systems.
Their new fluid is SL.6 and these are the benefits as listed on their website
Advantages of Original ATE SL.6
The nw SL.6 has a dry boiling point of 509°F (265°C) and a wet boiling point of 338°F (170°C)
While the dry and wet boiling points are only about 5% lower than their racing fluid, the trade off is a faster operating ABS system.
Below is the graph ATE uses to demonstate the advantages of the low viscosity SL.6
The other trade off is ATE recommends changing the SL.6 every two years where as their racing brake fluid was recomended to change every three years.
Seeing as I am not on the track, I would probably benefit from the quicker responding ABS system.
I also found another low viscosity brake fluid with a good following, Pentosin.
Interesting, the dry and wet boiling temperatures are identical to the ATE SL.6.
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