i drive an '86 westy with about 165k miles.  about 2 years ago, i
installed an autometer oil pressure gauge (270degree sweep, stepper
motor driven, pretty damn accurate).  since then, i have observed
relatively consistent oil pressure which agrees with most of what i
have read here (10psi per 1k rpm under load, 3-7psi at idle depending
on temperature).  however, on my last trip up to tahoe from san
francisco (200 miles & about 8,000 ft of climbing), i began to see
lower pressures while cruising on the freeway at about 70mph.  the
pressure eventually got as low as maybe 25psi.  i stopped to pick up
some supplies and did a visual inspection of the engine--no leaks,
good oil level.  the car was parked for maybe 20 minutes.  when i
resumed, the pressure was normal for about 10 minutes of freeway
driving and then began to drop again.

i made it up to the mountain, and back home, with no other problems.
since it was time anyway, i did an oil change, using the same as i
always have, mobil1 15w50 and a mahle filter.  for good measure i
drained the oil through a funnel with a stack of torroid shaped
magnets in the neck.  oil seemed fine, no metal particles stuck to
magnets.  went on a 65 mile drive up to santa rosa and saw the same
thing--oil pressure dropping slowly below what i'm used to, but
returning to normal levels if i parked and let everything cool down.
because i'm seeing normal pressure vs engine speed for awhile after
warming up the engine, it seems to me that this is possibly an issue
with my oil getting hotter than i'm used to, rather than excessive oil
flow through a worn bearing somewhere, which seems like it would
appear immediately.  would you experts agree with this.... or should i
consider this a pressure problem?  the cooling system is in good
shape--i went through this summer and put in all new hoses and tstat,
flushed and filled with vw blue coolant, bled extensively.
temperature gauge reads right in the middle, just as it always has.
only other thing i've noticed recently is that when i've been parked
for several days, the valve clatter on startup seems a little louder
than it used to, but it goes away after 5-10 minutes of driving.

if this is a problem with the oil getting too hot, what could be
causing it?  or is this consistent with what people see in old engines
that are starting to die?  and if this is the sign of excessive
bearing clearances, how long do i have before i spin one?  i'm mainly
trying to determine if this is a sign that i'm about to get stranded
in the mountains somewhere during the next snowstorm with a blown
engine.

thanks.

Ben.