coolant temperature fluctuating 180 F - 210 F

Just started up my Camaro Z28 1997 for first time after rebuilt engine due to blown head gasket by overheat (heads done as well).
I noticed that the temperature works its way up to 210 (180 thermostats), then slowly goes back to 180 just after some minutes, and then slowly back to 210 and repeating over and over.
1. I have bleed cooling system (both places)
2. Filled up with water after bleeding
3. Replaced thermostat with a new one (also 180)
4. No smell or leaks and no mist
5. No loss of water or leaks under car
Any ideas?

[@32Mark_]

What was the problem did you get it figured out

[@johnnyaberg9617]

LuhMaRk1 Yes, the short answer is that is not is a problem - as long temp not turn over 210. I found out that GM during some time used these exact gagues. Many customer was worried that it was something wrong with their cars so GM changed to idiot gagues later on that does not travel up and down like mine. So far I have driven 5000 km and all works fine. May also add that makes the temp go down is that the electronic fans turns on close to 210 and turns off after a while. This makes the gague pending.

[@32Mark_]

Johnny Åberg okay not sure if this pertains to me then. I put the 5.7 vortec in my 78 Malibu carb swap so i use a mechanic gauge mines does that fluctuate while driving. But does go over 210 some when i get on it going down the highway. Haven’t found out what it is yet

[@dallascalderilla4392]

Is 144 hot enough for my 5.3 engine