funny temp guage behavior

[Avrum Belzer <apb4419@idt.net>]

Hello all.  The water temp gauge on my S6 has changed its behavior recently.
Frequently it will not rise above the top of the warm up (first few marks on
the left) zone unless it is stopped at a light or in traffic.  Once moving
again it falls back to the warmup zone.  Until now it has always run right
on the normal line regardless of speed or ambient temp.  I took it to the
dealer but, no surprise, they had nothing to say after checking the gauge
and the actual water temp.  With the car in the shop it runs right on the
normal line as mentioned above so they say there is nothing wrong.  I know
something is going on.  I would like to know what.  Any thoughts or
experience?  Thanks.

APB
95.5 S6 wagon 18K