I noticed that one of my risers is getting very hot when I have the exhaust switch to run down to the outdrive. It appears to cool down just fine when I have the switchable exhaust on with exhaust running straight out the back. This happens on just one side of the engine. I also noticed that when it gets hot the 1" or so water hose going to the riser from the thermostat is hot as well. This is on the starboard side of the engine.

Why is this???

If the pressure is low, water will follow the path of least resitance.
Make sure you don't have a slipping belt, then that your impeller is good and last that you don't have something plugging the lines.

Mine was a slipping belt.