I noticed recently my '91 LS400 w/72k miles has emitted a small cloud of blue smoke on startup. A small amount, mostly from the left exhaust pipe (but some from the other side too). I recently changed the oil to Royal Purple 5-30. Doesn't happen every time, and not just after sitting overnight, can happen after only a few hours. Could it be sucking oil from the crankcase venilation system? Otherwise car runs fine. Smog test was excellent too.
any ideas?