UPDATE* well it turned out to be a bad thermostat and radiator cap
thanks carguychris i never read the very top sentence of your reply lol

i know this isnt a car on here but the grandam forums arent very helpful
im fixing my sisters 1999 grand am SE 3400 v6 i just replaced her thermostat because her coolant kept spewing out of the resovoir bleed line and sure enough her thermostat was stuck closed

well i throw it all back together bleed the air out through a purge valve by letting it purge bubbles until it runs water with no bubbles with the heat on 1 so the coolant runs through the heater core
there are no other leaks present

so i tighten the purge valve screw the resovoir cap back on all seems well then it starts pouring out water again through the resovoir overflow line

help?!?

It's probably a bad radiator cap. Other possibilities are:

1) If the radiator is metal, the surface where the cap screws down could be dented or scratched, which will make the cap leak. You can work the dent out using a hammer and punch, file or sand out the scratch, or simply smooth out the whole area with JB Weld. Also check that the ears on the back of the cap are actually holding the cap down tightly against the radiator. If not, bend them gently with pliers until they do their job.

2) Did the thermostat have a jiggle pin? This is a little two-headed pin that fits through a little hole in the outer rim of the thermostat. In an engine where the thermostat is a high point in the cooling system, the jiggle pin bleeds air bubbles from behind the thermostat as the coolant is refilled. If the thermostat has a jiggle pin, the thermostat must be installed with the pin on the uphill side (if it's not horizontal), and the coolant must be refilled sloooowly, because air can't move very quickly through the little bitty hole. Failure to follow these steps can trap air bubbles in the cooling system and cause overheating. [:(]

3) [edit] Did you refill the coolant with the car parked on level ground? If not, park it on level ground and try adding more coolant. Some cooling systems will not bleed properly if the car is parked on sloping ground.

What does the car's temperature gauge indicate while this is happening?

well its one of those gm systems where it doesnt have a radiator cap, the plastic coolant resvoir is the only entry of water and as far as the thermostat goes no jiggle pin
like on my focus' thermostat

the temp stays at 220 which is above the norm of its 200(middle)