This may sound like a dumb question, and I probably should know the correct answer, but I don't. So I'll just throw it out there.

I too always get the engine up to normal operating temp before I change the oil. But with 0W-40 weight oil, wouldn't the viscosity of the oil be at "0" thus making it more liquid (and easier to flow) if the temp of the oil was cold when you drained it?
On the other hand, if the viscosity of the oil is lower when it's cold, then why does my oil pressure gauge (in another vehicle) always read higher when I start the engine, and goes down as the engine warms up?

I'm not a Petro engineer, or scientist, so if any of you know the scientific answer to this question, could you put it in "layman's terms" so I can understand it?

Thanks