The critical thing about Castrol GT/LMA brake fluid is not the regulatory
test rating (DOT 4, DOT 5) or the performance specs (boiling point, etc).
It is the "solvent" chemistry -- Castrol GT doesn't seem to melt down the
rubber seals supplied for use in LBCs, as other brands of brake fluid
frequently do. Perhaps there is another brand that has the same
properties, but if so, it has not been identified. Possibly some brands
of seals are more resistant than others -- these have not been identifed,
either. Given this general state of ignorance, using anything other than
Castrol GT in your MG's brake system is a gamble. This bit of "folk
wisdom" was being passed around via word of mouth 20 years ago, and from
what I have seen on this list, is still true today.
Silicone fluids, which don't harm paint and therefore may be presumed to
be non-solvents, may be an exception. I don't have any experience with
them myself.
Terry O'Brien had this to say:
>...It seems that the popular opinion is that the only fluid to use is Castrol
>gtLMA. I think I even noticed someone putting down synthetic fluid.
>Why?
>
>When I stopped by my favorite parts house in order to purchase the
>Castrol 20/50 (I used syn blend) to put in my transmission after I had
>drained out that nasty Hypol crap that had been running in it for the
>past 23 years (yes, the above was tongue in cheek), I looked for the
>correct brake fluid to no avail. I found Valvoline SynPower High
>Performance Synthetic brake fluid. It says it has a low moisture
>formula which meets or exceeds DOT 3 &4, and has a boiling point of 333
>to 513 F. Our beloved Castrol is 311 to 446. Could I have stumbled
>upon a better product? What is so wrong with synthetic?
>
>===
>Terry O'Brien, RDU/NC/USA
>-'77 MG B (daily driver)
>-'82 Dodge Ram 50
>-'90+ various boring things
>-other people's British problems
>
>
--
Max Heim
'66 MGB GHN3L76149
Runs great,
looks particularly bad since some SUV clown backed into it.
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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