The radiator is an air to water heat exchanger, if air is not flowing across the fins of the radiator, there will be little change in temperature between the top hose (inlet) and the bottom hose (outlet), and only check the temperature difference between the hoses when the engine is running, fans are on, and system is closed (cap on).
When your bleeding the air from the cooling system, make sure the fans are "ON", turn the a/c on if you have to. Let the engine idle with the rad. cap off, add coolant as necessary to keep the radiator full, watch the coolant flowing out of the tubes (thermostat open), the air from the fans should be hot. Make sure there are no air restrictions in front of the condenser.
DONT shut the engine off with the pressure cap not installed. Dont hyper focus on small bubbles for the moment, get the system as full as possible, put the cap on and go for a test drive to bring the engine up to temperature. During your test drive pull into a parking lot, leave the car running, open the hood and take a temp reading of the top hose compared to the lower hose, top hose should be hot (min. 195) lower hose should be cooler at least 20 degrees or more.
No need to remove the thermostat for any reason, not even when testing for combustion gasses.
Hope this helps.
