Originally Posted by ChrisSlicks

Sorry that's not really true. Oil thins as it gets hotter and thickens as it cools.

The viscosity of a 5W30 at 100F is around 60 cSt, and at 210F is around 10 cSt (higher number is thicker).

I think you were mislead by the numbers. The number followed by the W means that it is a Winter weight, which means it has the viscosity of that weight oil if it were at operating temperature (210F), but doesn't mean that it acts like a SAE 5 weight oil would at operating temperature while cold.

Now with the modern multi-weight oils there are some properties that are built in the help reduce the extremes in viscosity, but not so much that it can ever be level in viscosity or operate backwards.