Ah, I see where you are coming from.
Multi-grade oil are indeed designed to "appear", or behave as different viscosities as the temperature changes. This allows them to stay thinner at cold temps but not go way too thin even once the oil is very hot. However even with these characteristics they are still much thicker overall when cold than when hot. A quick google search found this image:
http://lh4.ggpht.com/_TcZIHGRFnvY/Sx...c/s512/oil.jpg
From this site:
Graph your oils