Running temps.
 

I recently bought a 06 Ram 4x4. It has the 5.9. It's the first diesel truck I ever driven. I noticed that the temp gauge is alway moving. It bounces back and forth between 190-200. Is that normal?

yup.

Thanks. I was concerned a little because I'm going on a road trip next week.

Your just seeing the t stat open and close around 190.

Replace your thermostat...this is typical of a faulty (but not failed) thermostat...its termed "tick-tocking". It is "normal" to some folks, but it is not actually normal to the Cummins.

From a cold start, it should run up to just above your normal operating temps initially (until the thermostat initially opens), drop slightly below your normal operating temp (inrush of cold coolant from radiator), then settle down at you operating temperature...it should not move much at all afterwards (unless you're towing heavy).

I had an electronic gauge on mine, and could watch the coolant temp; the temperature doesn't fluctuate much at all when the thermostat is operating normally.