Temp Gauge Rising and Falling

[es8834]

I just got the Tensioner, Thermostate Asy, V-Belt, and Pulley replaced on my 1996 Ford Explorer. Had the Tensioner seise causing the truck to overheat. When I got the truck back, the temp guage is going from cold to normal while driving at strange intervals. The coolant color was normal on the repair. What could this be? Could the Bypass Hose (90 degree hose be leaking) or something else. Thanks

 

[TPLYNCH]

There could still be air in the system if it wasn't properly "burped". You can try replacing the radiator cap. The spring weakens with age and causes pressure
loss and fluctuating temp.

 

['97 V8]

does it hit cold or is it from a bit above middle to in between c and that temp gauge indicator in the middle. if its like that then its normal as its cycling. if its hittin C well i dunno bout that, may need to be burped or replace the cap.