Hi Jim,
All presently available Castrol brake fluids for Dot 3-4 use are synthetic.
Castrol GT LMA is a Dot 3-Dot 4 synthetic brake fluid. Fully compatible
with other Dot 3-4 fluids. It contains a mixture of "alkyl polyglycol
ether esters" & inhibitors. It has a wet boiling point of 311 F & dry BP
of 446 F. It seems to be the most widely recommended fluid.
Likewise Valvoline Synpower is a Dot 3-Dot 4 synthetic brake fluid.
Fully compatible with other Dot 3-4 fluids. It contains "a mixture of
glycol ethers, polyglycols, & inhibitors". It has a wet boiling point of
343 F & dry BP of 446F. Not to be sacrilegious, but this particular
Valvoline fluid is equal to GTLMA in all ways, is fully compatible, &
has a slightly higher wet BP.
There are also several other fluid brands of equal composition,
compatability, & performance.
None of the above would work well with old natural rubber Girling rubber
parts, but these parts would only be available as very old NOS & really
not satisfactory for any current use in the first place. All newer
rubber brake parts are synthetics, even Girling rubber for at least the
last 20 years & will work with available modern fluids,
DOT 5.1 is a polyglycol based fluid, with a higher boiling point, &
is compatible with DOT 3-4 fluids. Not to be confused with DOT 5
silicone fluid. The numbering system is a bit confusing. DOT 3,4, & 5.1
are polyglycols, DOT 5 is silicone.
Many car makers recommend DOT 3-4 fluid today because it has lower
viscosity than DOT 5 silicone & works much better with the rapidly
cycling ABS systems. Silicone is too viscous to work well with ABS
systems at cold temperatures.
Some folks feel that since the polyglycols absorb moisture, which is
removed when the fluid is changed they are better than the silicones
which do not absorb moisture & allow it to collect in the low spots of
the system & cause rust. The pros & cons are argued endlessly.
To sum it up, the Castrol synthetic is a perfectly normal standard
fluid. No fear.
Dave Russell
Healey Bruce wrote:
>You describe it as synthetic, but you don't mention whether it is DOT 3, DOT
>4, or DOT 5.
>
>Bruce Steele
>
>From: "James Shope" <healeymanjim@hansencc.net>
>
>
>>rebuilt a servo and went to buy a quart of castrol. all they had was the
>>new synthetic castrol(which went from 6 to 8 bucks). As my book says "use
>only Castrol brake fluid or your system will surely perish". i do not want it
>to perish or go "tango uniform" using this new stuff. TIA hjim
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