Marty,

This syndrome has also been occuring on my 86 Syncro.  Here's what's
happening.  The oil pressure is in fact marginally low while the oil is
cold and thick, as occurs at start up at lower overnight temps (for me,
under 60 F).  I posted this issue to the list a few weeks ago and received
a flood of replies.

The consensus seems to be to use an official VW oil filter, as Fram and
other brands don't have enough filtering material, so there isn't enough
back pressure developed from the filter, and so not as much oil pressure is
available for the engine.  Some people said to always use 20-50W oil, but
they are from warm climate areas, so if you live North, that isn't
feasonable during the winter.

There are actually two separate oil pressure warning sensors (switches).
VW figured that there should be more pressure at higher rpms, so they
divided the sensors into one that works at low rpms, and one for higher
rpms.  The high rpm sensor is actuated at about 2500 rpm, which is why you
won't get the warnings at idle, only after you start driving and exceed
2500 rpm.  The one that creates your problem is the high rpm sensor, which
is called the .9 bar (millibars of pressure) switch.

Just for fun, start the engine cold, accelerate (while driving, not stopped
in neutral, as the load on the engine may also be a factor) to about
2500-3000 rpm, notice the warning light/buzzer, and then drop down to 1500
rpm.  The warning will probably go off.  In a short time, the engine will
be warm enough so that the oil is thinner, and the pressure will go up to
the acceptable range, and the warning will go off of its own accord.

I took my 86 Syncro to my local (WestsideVW) dealer, who has a well
deserved reputation for excellence, to check out the function of my .9 bar
(high) switch.  The mechanic told me that the switch (sensor) was
functioning fine, and that the oil pressure at cold starts was only
marginally low.  His advice was to use 10-30W oil (not 5-20W) for the
winter, and to warm up the engine a little at idle prior to driving in the
morning (which is a good idea for many reasons).

I hope this answers all of your Qs and lets you know that your system is
okay and that all you have to do is use the proper oil and filter, and warm
it up in the morning.  Or, you can do nothing and just ignore the warning,
as it really isn't harming things anyway.

Please write back and tell me if this covers everything.  If not, I saved
all the list responses I received and I could copy them to you.

Budd Premack
86 Syncro, 84 Vanagon, 73 Super
Minneapolis, MN
bpremack@wavetech.net