Robert Carley writes:
> Is it safe to add DOT 4 to DOT 3 that is already in the
> brake system?
Yes. DOT4 brake fluids, to the best of my knowledge, all begin life
from the same base stocks as DOT3 brake fluids ( ethylene glycol ). The
major difference is the addition of borate esters to the mix at some
point, which raises the wet and dry boiling points, and may be a factor
in inhibiting absorption of water.
> I just re did my rear brakes (cylinders, etc.) plus various
> brake lines,
> and cannot remember what DOT I put in the car when I
> replaced the master
> cylinder two summers ago.
Mixing the two fluids will probably give you a DOT3.x solution, with
characteristics somewhere between DOT3 and DOT4. Spring is a good time
to change brake fluid, in any case, and 2 years is about the point where
the brake fluid has absorbed as much water as it can hold. You may well
benefit from flushing the old stuff, and refilling with DOT4.
Stuart Steele
|