overheating

:runaround: my 94 grand am 3.1 is overheating. As soon as i release the overflow cap and release the pressure it seems to be fine again until it builds pressure. Is it my overflow?
thanks

It could be many things. IS there bubbles coming up into the overflow tank? Is there any coolant in the oil or oil in the coolant? How's your thermostat? Is your fan coming on? There are many possibilities here. Good luck...