Different versions seem to have different systems.
"Just for interest if you fit and aftermarket digital oil temp gauge the warning light comes on much earlier as gauge has a different resistance. (Also gives you a panic attack!) I looked this all up when my original gauge died and wanted digital/accurate replacement"
Yes, I had that panic attack & it was a short while before the penny dropped. I circumvented the problem by tucking the original gauge in the void behind dash until I could resolve the problem properly. That was 18 months ago, you can get a lot more interesting stuff done in 18 months than to work out a suitable resistor to overcome that particular issue.
M