Bad thermostat?

[2004silverado5.3extcab]

I've got a 2004 Silverado with the 5.3. Here recently my thermostat started acting different. When I take off down the road it'll be just below 210 like normal, and it suddenly jumps up to 260 or so which is redlining. It'll stay there for a few seconds then go back down to 210. Could this be a bad thermostat? What else could it be?

[sefiroxx]

Thermostat are slow adjusting - once hot, they'll stay open. Sounds more like water pump or air in the system

[04BlackMagic]

Bad coolant temperature sensor or bad coolant temp stepper motor (Gauge) The coolant temperature is located in the block. I am unaware as to where exactly. On these trucks, the stepper motors are a common failure. Does the engine overheating light come on when past 210? Also, how many miles on the rig?

 

 

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