92 Claret Head Gasket Replacement Temp Gauge Fluctuates

[dibenso4]

Hey guys haven't been on in a while. Just finished a head gasket job on my 92. It drives great so far, engine seems sealed up well, no leaks, amr radiator. The only problem I'm getting is a fluctuating coolant temp gauge. Every now and then it raises to a little under 3/4 of the way up on the temp gauge, then slowly goes back down to exactly halfway, I know the normal running temp is just under half. Let me know if you guys have suggestions. One thing to note is the thermostat is a "heavy duty" Motorad thermostat from rockauto. The way it overheats then cools down, there's almost a pattern to it. It's still drivable but I don't want to damage anything right after a hg job.