> 
> My friend's 1988 vanagon has low oil pressure, when ideling and not when
> accelerating or traveling fast.  He DOES have 20w50 weight oil in his
> vehicle.  He brought his van in to a shop and had a gauge hooked up and
> indeed he has low oil pressure, so the switches are not at fault.  The
> problem gets worse as the engine gets hotter.  

What kind of oil filter is he using ?
My guess is he is using a Fram. If so replace it with another brand.
Make sure it has the pressure relief valve inside. Look inside the 
center of the filter. if it is plain it does not a have the valve. If
it exist you will notice it.
Replace with new oil. Let us know if the problem goes away before he
tries doing other things.
It is common knowledge among us who are on the list awhile that Fram
filters are unsuitable for Vanagons. Another experience is Champion 
brand spark plugs. Twice I bought plugs for my mercedes and VW and
one in the pack of four was bad. I just dont know whether it was my lousy
luck or their quality is that bad. From now on I just use NGK or Bosch
even though they cost much more.

 
>