[Vwdiesel] Oil Pressure Testing on an '84 Bunny

[Bryan K Walton]

Sorry for the long email,

Just over a month ago, I started a thread on this list seeking some
explanation of the VW Rabbit oil pressure warning system.  I was a
little unclear about how it all worked and pieced together.  The
reason why I was initially curious is because, like many other people
who have owned bunnies through the years, my oil pressure idiot light
comes on when the car is idling AFTER the oil starts to get warmed up.

I've been using 15W-40 in it, but that light had me wondering whether
I needed to be moving to a 50 weight oil.  On the advice of others, I
decided the first thing to do was to get an oil pressure tester and
find out my actual oil pressure. 

I removed the pressure switch from the cylinder head and screwed in my
new testing gauge and then looped it around the car and in through my
window and then took the car for a spin.  The car was not completely
cold when I started but, still, I drove it for about 40 minutes at
mostly highway speeds (55mph) to get the oil warmed up.  I left the 
switch at the oil filter still connected.

Results: I THINK my oil pressure is fine.  Toward the end of the 40
minute drive, here were my psi readings (I don't have a tach, so I
know this won't be ideal, but this is the best data I can collect):

Idle = 20 psi
15 mph = 40 psi (2nd gear)
25 mph = 38 psi (3rd gear)
35 mph = 35 psi (4th gear)
45 mph = 48 psi (4th gear)
55 mph = 60 psi (4th gear)

My tranny code is 4A (which I can't find much data on), but it is a 4
speed manual transmission with the 3+E gear selection.  (This is a
1984 bunny.)

Bentley says that the minimum allowable pressure is 29psi at 2000
rpms.  Now without a tach, I don't know what my actual rpms were, but
it still seems like my pressure is fine.  Sure, perhaps there may be
others with higher pressure, but this seems to be within spec. Am I 
correct in this assessment?

Now, here is my final question: with my warmed up car idling and my
oil pressure at 20psi, my oil pressure idiot light was still coming
on.  Can I infer that my oil pressure switch located at my oil filter
is probably faulty and should be replaced?

Thanks!
Bryan