One easy way to vent air from the cooling system is to drill a small hole (1/16"+ -) through the flat area on the thermostat. This will allow small air bubbles to bypass the thermostat while it is closed. Some thermostats incorporate this air bleed feature in design, labeled as a "jiggle wire" type, which closes the bleeder at high flow.
Since you already have an IR heat gun, i would check the temp at the top of the radiator, right at the location of the upper hose location and compare the temp reading at the same area near the lower hose. This temp differential will determine your radiator/fan efficiency in heat rejection. Test this when you are at op temp or a little above. Work safe!