Thermometer check on RAM2500?

Thanks to all whove tried to help out on my antifreeze/overheat issue. The
truck will be at the shop on Monday since I'm at a loss...

In the meantime, can someone tell me where the thermometer is located, and
how one would check it for leaks/problems? Its mostly just curiosity, but
I'd like to know.

Oh, and to keep everyone interested up to date, I ran the engine for about 5
minutes today to check a suspected leak -- no dice. I did notice that the
radiator stayed cool while running, but got really hot when I turned the
engine off.