Oil pressure is provided by the oil pump and maintained by the gaps in the bearings.
So oil pressure is not based on engine "load", i.e. going up hill or down hill, it is based on revolutions of the oil pump, so engine RPM.
At 2,000 RPM oil pressure might be 25psi on a warm engine, 30psi on a cold engine(oil is thicker when cold)
Going up a hill in 2nd gear at 2,000 RPM or running on flat ground in 4th gear at 2,000 RPM would be the same oil pressure, it is RPM based.
As far as the oil itself, 10w-30 means the oil is 30 "weight"(viscosity) at 212deg F, normal engine operating temp.
At freezing temp a 10w-30 oil acts like 10 "weight" when cold, thinner than 30 "weight" would be at freezing temp but still thicker than 30 "weight" at 212deg F.
So oil is always thicker when cold, no way around that.
So to give yourself piece of mind run the correct multi-"weight" oil for your winter conditions/temps.
Toyota or oil makers provide the information for outside temp ranges and what oil is best.
You could also get a remote starter for your car, or a block heater, either would work to have the engine pre-heated before you start driving.
But I wouldn't worry about blowing a seal because the engine is cold, if it happens it would have another cause.
Last edited by RonR; 11-11-2012 at 04:36 PM.