captiva, cosworth engines are known for high oil consumption, even when new. I am pretty sure that 1 litre / 1000km is normal.

See here: https://passionford.com/forum/viewto...ht=consumption
and here
https://passionford.com/forum/viewto...ht=consumption

I can't comment on the tests you've performed, I am not knowledgeable enough, the only thing you don't mention though, is which oil you use