06 cummins temp gauge fluctuating
 

While its good and hot the dash gauge will drop to prob 160 then hang there for few seconds then shoot back up to around 200 then in a bit drop again and repeat. But my digital temp on my quadzilla rail pressure gauge stays right around 200-210. Think the thermostat or water pump messing up? It's prob been a year since they both were changed.

Your should run pretty close to 190 while cruising you may have a thermostat issue or your low on coolant and are getting hot air pockets. The water pump should last longer than a year.

Ok thanks. I'll get another thermostat and try it