> I got an answer from
> Castrol tech support which suggests the issue *may* be the use of GF-4 oils,
They may have a point. The GF- ratings are for cars with catalytic converters,
and limit the amount of various substances, including zinc, that can be in the
oil.
> lists 8 types of Castrol (including GTX) with "more zinc than the SG oils
> marketed during the muscle car era", and 6 types equal to the SG level.
I'm suspicious of that statement ... for one thing, the API service levels do
not specify how much zinc should (or should not) be present, they only give
minimum performance standards. "Higher quality" oils were free to include more
zinc, with the result that there was something like a 2:1 range in the amount of
zinc present in "SG" oils.
For another, Castrol GTX is, according to the Castrol web site, a GF-4 oil. So
first they say the problem is we are using a GF-4 oil, and then they recommend a
GF-4 oil for us to use. Something's rotten in Denmark.
Then of course there are other additives involved that serve overlapping
purposes with ZDDP. Even ZDDP isn't pure, it's a mix of several different
chemicals which may or may not have different levels of effectiveness and/or
different amounts of zinc.
There are other reasons I distrust Castrol, but those will do for now. You
can't hardly expect them to say "Our oil will ruin your engine", now can you ?
> I had been trying to find a comparison / timeline on the different
> historical
> API grades. Anyone know of one?
Here's one. Don't know how accurate it is, tho.
http://www.sizes.com/materls/engineOil.htm
Randall
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