Bubbles in Coolant Expansion Reservoir on 1998 Ford Ranger

I recently flushed they system and changed the thermostat. There is no coolant loss from hoses, water pump or otherwise. Only bubbles after I turn the car off (will not bubble while running). Can't see / smell anything abnormal in the expansion tank. Seems to be extra pressure in radiator after car has cooled... When I open the cap it does not smell like coolant (sweet).

Asked by for the 1998 Ford Ranger
It may just be air trapped in the engine from the coolant flush. Is everything else normal, the temperature OK and is the coolant level dropping?
so how doo you get the air out of the cooling system. Is coolant WATER?