From what i have read, the oil rings on my engine, N52B25O1, are thinner and carbonize faster and therefore uses more oil.noiseboy72 said:2.5 and 3.0 are essentially the same engine just with a slightly longer stroke.
Just for the record, my 2.5Si uses about 500ml per 1000 Miles - and more if I am really pushing on. It doesn't smoke, has no issues with emissions and I run it on 5W30. A low ash oil prevents a lot of the carbon deposits and the higher oil smoke temp compared to a mineral oil will help as well.
I did try it on 10W30 to see if this would reduce oil consumption and it made virtually no difference. I would stick with the published viscosity and just change the oil at the correct intervals.
The engine that came in '07 with a black cover have different oil rings and do not have this problem.
This is however just info from Google, and i could be wrong. But it sure is a plausible explanation.