More modern cooling systems than stovebolt engines incorporate various types of internal coolant circulation when the stat is closed. Small block V8's have an extra hole in the block on one side of the water pump that allows a small volume of coolant to circulate and eliminate the hot spots around the cylinder walls. Other engines have a fairly large passageway directly below the thermostat that is closed by a disc on the bottom of the stat once it opens, redirecting the flow toward the radiator.

The idea behind creating coolant flow past the cylinder walls and back to the thermostat is to reduce or eliminate the possibility of coolant boiling around the cylinders and creating enough pressure to override the pressure spring in the radiator cap. This can happen in a matter of a couple of minutes or less if the coolant doesn't circulate inside the block and cylinder head.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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