Mobil 1 does not come in a 15w-40. Do you mean 15w-50? Those pressure readings are not that bad and close to spec. The wear limit is 28 psi @ 4k rpm. You should have a lot of time left. What would add value is an oil temp gauge. Then you will see why you have pressure concerns. 

Dennis, 
From my phone.

-----Original Message-----
From: "Stuart MacMillan" <stuartmacm@GMAIL.COM>
Sent: ‎7/‎15/‎2013 2:43 PM
To: "vanagon@GERRY.VANAGON.COM" <vanagon@GERRY.VANAGON.COM>
Subject: I'm going to disconnect my oil pressure guage

Ignorance is bliss, at least for a while.  My worn 1.9 with 140k miles runs
5-8 psi idle after a run on the freeway, and 22-26 psi at 3000 rpm when hot
with Mobil 1 15w-40.  Pressure is 60 psi at cold start up. This is in nice
temps, about 70 degrees, and mostly flat terrain.  I knew it was bad, but I
just want to get another 2000 miles out of this engine, and I'm staying on
the NW coast this summer to avoid long climbs and hot weather.  I wonder if
20w-50 would boost it a little.  STP?  Or just forget about it?

What do you think?

Stuart