Cooling System Problem

[trg-42]

I have a stroked 351W in my Superformance. Lately, I the coolant temp ( typically 180 to 210 ) spikes up to 240 and instantly back down

Temp sender is in manifold crossover. Is it possible that the coolant is not flowing ( stuck thermostat ) then flows?

IT has been getting progressively worse now where temp stays at 210 but occassionaly spikes up to 240

Before take out the thermostat housing I want to see if any of you guys have other ideas

Thanks

UPDATE

I replaced the thermostat housing ( and new thermostat with the hole drilled in the top ). Filled it to the top from the sender port and thermostat housing port

I'm suprised how much more coolant the system took. Leads me to believe that there was a hell of a air pocket in there

Strange how the system would over the past 3 months "suck in" air. I think it was from the small leak around the thermostat housing as it cooled

Took it for test drive and temp never got over 190, even in traffic

Thanks everyone for the advise !