obviously, im confused. two thoughts. if the coolant is actually bubbling like a geyser, that suggests that the headgasket or block, etc went bad, and combustion pressures are getting into the coolant.
if it spits coolant out, is it comin out the rad neck (runnin with cap off) or out the overflow? with the cap on, do you notice that no coolant from the reservoir is being used, etc? the cap could be toast. with cap probs, ive seen/heard cars that make "bubbling" noises after the car is turned off. also, as mentioned, the coolant cant overcome spring pressure to put fluid in the reservoir. some with "weaker" cooling systems run a lower pressure rad cap.
one of these or none may apply, as im confused (not you, im just tired).
to anwer your original question, ill share what i know. when i did my cooling system once over on the 88 gt, i flushed coolant and did a new stat. i jacked the driver side, front end of the car, to get the rad filler neck to be the highest part of the cooling system, so help purge cavitated air. i filled it all up with the new juice. i ran it with the rad cap off. warm it up. when the stat opened, the coolant in the rad started flowing from pass side to drivers side. the level in the rad went to an inch or two below the neck, and no higher. it burped a little at first, and i added coolant. then stabilized. stayed at this level indefinately.
so thats how mine operates, if it helps give you a lil' basis of what (may) be normal.
good luck.
