Bruce K. Please show the dated front page of the Service Manual you show above. I have 6 Manuals plus electronic copies & none show that page.

 

My photocopied service manual has the same lubricants table as Bruce's. As I wrote a few weeks ago, I don't know the exact date of publication. Either it fell off the bottom of the photocopier or BL couldn't be bothered. At latest, it's 1976 when the library stamped it, but later than yours as it has Jaguar Rover Triumph named on the front (a BL historian could probably date that).

By contrast, my original owner's manual (1963) and chassis plate are consistent with the lubricants info on the chassis plate of the old racer.

I wonder if some BL person updated the lubricants chart to what he considered good, modern practice. The worlds of Austin and Triumph are/were very 20/50 oriented.

 

I would say the British were very SAE 20W-50 orientated.

Whereas the Americans went for lighter grades. e.g. 1957 Chevrolet.