When you do that (cooled off), have the radiator cap off and the right side higher than the left (curb/jack/etc). Make the overflow bottle the highest point in the system to allow trapped air to escape. I don't think it's stuck in your heater core (should hear gurgling from behind the dash).
From the free Chilton's Manual:
2.Fill the degas bottle to 25 mm (0.984 in) above the COLD FILL line.
3.Install the degas bottle cap until at least 1 audible click is heard.
4.Turn the climate control system off.
5.Start the engine and increase the engine speed to 3,500 rpm and hold for 30 seconds.
6.Turn the engine off for and wait for 1 minute to purge any large air pockets from the cooling system.
7.
WARNING
WARNING: Always allow the engine to cool before opening the cooling system. Do not unscrew the coolant pressure relief cap when the engine is operating or the cooling system is hot. The cooling system is under pressure; steam and hot liquid can come out forcefully when the cap is loosened slightly. Failure to follow these instructions may result in serious personal injury.
Check the engine coolant level in degas bottle and if necessary fill to 25 mm (0.984 in) above the top of the COLD FILL LEVEL on the degas bottle if the engine is warm or to the top of the COLD FILL LEVEL if the engine is cold.
8.Start the engine and let it idle until the engine reaches normal operating temperature and the thermostat is fully open. A fully open thermostat is verified by the cooling fan cycling on at least once.
9.Increase the engine speed to 3,500 rpm and hold for 30 seconds.
10.Allow the engine to idle for 30 seconds.
11.Turn the engine off for 1 minute.
12.Repeat steps 9 through 11 a total of 5 times to remove any remaining air trapped in the system.
13.
WARNING
WARNING: Always allow the engine to cool before opening the cooling system. Do not unscrew the coolant pressure relief cap when the engine is operating or the cooling system is hot. The cooling system is under pressure; steam and hot liquid can come out forcefully when the cap is loosened slightly. Failure to follow these instructions may result in serious personal injury.
Check the engine coolant level in degas bottle and if necessary fill to 25 mm (0.984 in) above the top of the COLD FILL LEVEL on the degas bottle if the engine is warm or to the top of the COLD FILL LEVEL if the engine is cold.
14.Install the degas bottle cap until at least 1 audible click is heard.
