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The old Castrol GTX-2 (no longer sold) was replaced by Castrol GTS 20/50 (white bottle). It has lower zinc/phosphate content, in line with the SM/SN standard. 800ppm is now the upper limit, so modern catalytic converters are not poisoned.

Castrol themselves recommend Edge, but this is a synth (IIRC), and the general consensus is that full synth oils are too slippery for old (or old-style) gaskets and you get leaks.

I use the Penrite HPR30 20w/60. See Penrite's statement on zinc content at: http://www.penriteoil.com.au/tech_pdfs/149%20LATEST%20ZINC%20LEVELS.pdf and also http://www.penriteoil.com.au/faq.php

(No affil., just a satisfied customer).

The SOC guys in the UK recommend Valvoline VR1 racing oil
although I don't know how readily available it is in Australia/NZ, although it appears to be on sale.

This is worth reading on VR1 as well:


I think just a good quality mineral oil with at least 1,000ppm zinc will be fine. Castrol did specifically advise one Stag owner recently that GTX was not suitable for flat-tappet engines like the Stag V8.

I'm sticking with a high-zinc mineral oil and doing regular 3,000 mile (4,800km) changes. The Stag V8 can produce a lot of dirt, so the more frequent the oil changes, the better. Of course, fresh oil also keeps the whole thing cooler. But none of this will be news to you as a long-time Triumph owner.


'77 Triumph Stag Mk II Pimento

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The SOC swear by VR1 sold at Euro Car Parts.

I have so far used Millers Classic 20W50 in addition to Unipart M300 20W50.  Both have given me no issues so far.  What made a larger difference IMO was going to a spin on oil filter.  Maybe it was a coincidence but my oil does seem cleaner upon fitting it (I have now changed my oil twice in the Stag).

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