Temperature gauge jittering ?

[rwh531]

Recently replaced my Thermostat and water pump and radiator cap now I notice the temperature gauge jitters around regardless of if the engine is cool or warm. there is also a pinhole leak in the radiator near the oil cooling inlet hose.

Before I get a diagnosis/opinion I feel I should state the radiator has that Bars Copper flake stop leak in it and I tried to patch the leak on the outside using JB Weld (neither of which worked) 

 

My theories are

#1 The Stop Leak has somehow stopped the thermostat from completely closing or the thermostat was faulty when installed  (thermostat been installed for a month and this problem has only been happening for 3 days)

#2 the radiator leak is causing it (yet again the leak has been present much longer than the gauge jitter.

#3 there is air stuck in the cooling system.

 

Going to replace the thermostat this weekend  and the radiator within the next month but wanted to ask is there anything else that could be causing this issue