Time for some diagnostic work I'm afraid. In my ten years of owning my 90
Westy I have never had this warning activate. It went off just yards from my
 driveway fortunately (thank you Van Gods). I checked it again this morning
and  it does magically activate at 2200 RPM's. I have perused that Archives
and will  set out to check all of the wiring and also for leaks at the
sensors. Of course,  I have 15w-40 Mobil 1, correct oil level , Mahle filter and
no apparent issues  with the oil itself. Quick check doesn't show any
corrosion at the connector  that splits off the wiring to each of the sensors.
Not looking forward to  possible removal of exhaust nuts to remove the engine
tin. I have had some sort  of slow oil leak from behind this tin so I'll
check this too. Wonder could it be  a leaking sensor? I had the van up on a
lift cleaning off dye in the AC for a  known leak at one of the condenser
connections (another frustrating problem now  secondary to this frightening issue
) then after driving about 15 miles  home it went off and my heart sank.
Just don't have the money in the budget for  the Subi 2.5 transplant yet. The
only other likely possibility not near the  engine area that might explain
this issue is the sometimes problematic 14 point  ribbon connection at the
speedo that is very fragile with a broken corner of the  plastic that the
ribbon folds over and the connector slips on to. According to  the archives this
connector carries the wiring from the sensors. Guess its time  to get her
up on ramps (don't want to drive back to work to use the lift should  I have
a true oil pressure issue) and scrape the knuckles and try not to use my
outside cursing voice. The engine was rebuilt about 100,000 miles ago by The
Bug  Shop in Blacksburg, Va. -Plug for the Bug Shop and Jewel the
owner-excellent  rebuild IMHO. It was broken in on conventional Dino oil for the first
10,000  miles and then nothing but 15-40 Mobil One. Oil changed every 7,000
miles and  filter change every 3500 miles. I'll report back on my findings.
Got to have her  ready for the trip to the Outer Banks without breaking the
bank in two  weeks.

David  Clarkson
1990 Westfalia