Figgidy temp gauge

[duckdog27]

I put in a new thermostat and coolant temperature sensor today to fix a "lively" temp gauge. After putting both of them in and running the truck the temp gauge still bounces from N to M. What the heck is wrong? I appreciate any info because I am stumped.

 

[Blee1099]

Sounds like you have air in the system.. purge it by starting the engine and letting it run without the cap and then fill it to the top..