If you get low oil pressure indications shortly after switching to a
thinner oil and you had none before that, I would think just go back to the
thicker oil.  If you're worried about 'cold start' or cold temp operating
issues, take a little more care on start up...don't just hit the key and
pop the clutch or floor it in drive...Take it easy for a few miles.

  I have Autometer gauges in my inline VW motor...both Oil pressure and Oil
temp.  Watching the two, I see it takes a few miles of running before my
oil arrives at it's normal operating range...pressure and
temperature-wise.  I put in some thinner oil for a short time and didn't
care for the way it behaved.  I consider oil pressure a very important
thing...I want it to be right...with the thinner oils I've seen my high
speed high load uphill oil pressure below where I like to see it...60psi,
more or less.  My hot oil idle is about 18psi...with 15-w-40..with 10-30 it
drops  a few lbs psi at idle and like 10psi at speed.  A long steep uphill
at very high speed really does translate to hotter oil and a drop in oil
pressure.  I didn't like that with thinner oil...

  Oil temp is very influential on your oil pressure....On startup, my OP is
very high no matter what the viscosity of the oil.    Thick or thin, it
doesn't seem to make much difference in how fast the oil gains temperature,
either,  but once up to operating temp..it does matter...thin oil gives you
lower oil pressures..