recommended oil weight?

Just wondering what type of oil you guys are running in your diesels?

I don;t have an owners manual. What does the book say?

I have been running with Duplex (Petrol or Diesel usage)15/40. Changed every 5000km
Bought economically in a 25 ltr drum.
On the Rocker Cover on my 2.8ltr 3L engine, it recommends SAE30.
On turbo engines I have heard that part synthetics are best.
I'll have a look at my manual when I get the chance.

I'm using synthetic 5/50 and it seems to run very smooth. I believe the synthetic is good for many more miles than the regular one. I remember many years ago when they first came out, they were doing tests on engines going 100,000+ miles and taking the engine apart and seeing no appreciable wear. Of course now, they recommend you to change much more often, but I believe you don't need to. I plan to change the filter at regular intervals, but only change the oil annually.