In my experience, THICK has always solved the problem.  High-speed driving
has often led to oil warning buzzer and light going off as I'm returning to
idle on exit ramp.  Switching to 20W 50 solved the problem.  Oddly, though, I
found that topping off the AMOUNT of oil tended to cause the problem to
re-occur.  (Anybody got an answer on that??)

So my solution has been to use 20/50, year round, and not to worry about
being half a quart shy.

Sam

'89 Carat
'91 Carat