This probably means the viscosity of the cold oil is allowing the pump to
overwhelm the pressure relief valve that's suppose to limit oil pressure
to something like 60 psi.

I had a '78 BMW 635csi that had low oil pressure so I ran 20w50 Castrol in
the summer and locked the oil cooler thermostat open.  I forgot to change
to lower viscosity and remove the thermostat lock one Fall and on the
first cold day it blew the large O-ring right off of the oil filter
canister.  It seems the oil cooler was after the filter and before the
pressure relief valve...