OK, here's the latest:
I noticed the smoke puff was much worse after idling for a while at a stop light. So today when I got home, engine nice and hot, I let it idle for several minutes. I then stomped on the accelerator and let off (let it rev to ~3k then back to idle). There was a BIG blue cloud that reeked of burning diesel oil. Revving it a second time (or 3rd or 4th), without idling, produced minimal smoke. Then I let it idle a few minutes, repeated the revving, and got another big cloud.
So it seems that at idle, oil is building up *somewhere* and then burns out in a cloud under load. At full throttle the smoke is minimal, or at least not very noticeable in the mirrors. Ditto when cruising.
I'm still thinking one of these three:
1- Blowby through the PCV into the intake elbow: But, blowby would get produced under load, not at idle - and not THAT much. There is seepage at the valve cover PCV grommet but I don't think it's indicative of anything significant. (Yes, the seal is recent and still soft.)
2- Turbo oil shaft seal: The oil pressure would be fairly high even at idle (~2 bar hot), producing the same leak rate as under load. (?) I guess it could be puddling up in the intake side, and then when the engine revs, it gets sucked in and burned. The reason I think this is NOT it, is that I didn't have this problem before the head replacement, and I didn't mess with the turbo while the head was off.
(Note: Another reason I suspect #1 or #2 is that the intake charge pipe has quite a bit of oil in it, but I'm not sure if it's more than "normal".)
3- Valve seals: Aren't the symptoms described above a classic case of bad valve seals? It might even explain that oil leak out the exhaust (which is mostly because the gasket didn't seal, probably warped manifold). But the valve seals were brand new on a new head & new guides! What could have gone wrong??
Any ideas welcomed, as usual...
Regards,