I think you have to call Castrol and ask for their data sheets. Haven't seen Castrol voluntarily post anything anywhere. The latest GTX SL info they sent me was dated 6/02.
5W20 5W30 10W30
Vis 100 C 8.8 10.7 10.7
Vis 40 C 50 63 72
Vis Index 158 160 142
HTHS 2.8 3.1 3.1
Flash C 204 204 213
Pour C -30 -33 -30
I also requested the MSDS sheet for the 5W20 oil. It's main ingedient is listed as a "highly refined petroleum basestock," followed by 15 different CAS #'s: one 64741, nine 64742, and five 72623 series numbers.
The additive package consisted of 10-30 %
a) zinc diakyl dithiophosphate,
b) calcium salts of alkylated phenolsulfides,
c) alkylated diphenylamines,
Plus 7-13% Methacrylate polymer and/or ethylene propylene copolymer with a nitrogen functional group blend.