4KS erratic oil pressure

[Larry Smeins <lsmeins@ball.com>]

I took my sons 84 4KS to work yesterday, 80 miles, as a test of my cam
cover gasket repairs.  On the way home I glanced down at the oil
pressure gauge and it was reading only 2.5 bar at 3000 rpm, normally it
is 4 or more.  When I dropped it to idle the pressure dropped to 1/2
bar.  I decided it was time to get some fresh oil in it and continued on
with plans for an oil change this weekend.  When I got home, after about
5 miles of slower driving, idle pressure was back at its normal 1 bar.
I assumed the oil had cooled but decided to see how the pressure
followed rpm.  I started increasing rpm and pressure increased normally,
the gauge went up in jumps but that I attribute to a dirty sender, until
it hit a little over 4 bar where it abruptly dropped to 2.5 bar and
stayed low all the way back down to idle at 1/2 bar again.  I suspect a
sticking or defective oil pressure bypass valve if the VW 4 has such a
thing.  I've never been into a water cooled VW so I need to do some
studying.  I'm looking for someone that has seen the symptom I saw that
can give me a BTDT report or any advice on what may cause the problem
and how to get at the pressure relief valve if my diagnosis is correct.
Is it part of the oil pump?  Can I get to the oil pump without removing
the engine?  Any help will be appreciated.

TIA

Larry
If you don't care where you are, you ain't lost