Quoting Graham King: db, 100 sounds really hot for normal running, I suspect the gauge isn't that accurate as at that temp the fan would be on permanently. It should run at (or around) the stat opening temp. I have a K and it runs about 80 (I have an 82 degree stat). The gauge and the fan work off different sensors, the gauge sensor is in the water rail, the fan sensor is in the rad.
The fan won't necessarily run when the engine is at that temp due to the fan sensor being in the position you describe. If coolant isn't circulating through the rad (for whatever reason) the engine will heat up but the fan won't run as the coolant there is still cold.