1996 Mercury running hot

Im stumped, I have a 96 Mystique 2.5liter V6 24 Valve Doch with 82K original miles on it. Heres whats goin on, A few weeks ago i was driveing and all of a sudden the temp gauge went all the way to red and started shakeing, i drove home. The radator light came on and the temp gauge went all the way to red and stayed there, even when i turned the car off and turned it on the next morning. I went and bought a thermastat, installed it, added coolant, still runs hot. When i drive it i noticed after about a half mile of driveing, after reaching operating temp the coolant comes past the max line then starts bubbleing and hissing in the run-off tank, The coolant when the engine is cold goes back to the normal "max" line, but when it gets hot it comes all the way up to the cap and it hisses and steams. Possibly a water pump? I of course dont bring my cars to dealerships so please do not just say bring it to a shop, i just want your input. Thankyou

I also forgot to add, The heater blows cold now.

I think you blowed a head gasket you should be blowing white smoke. Put a pressure gage on the radiator cap if the head gasket is bad the gage will pulsate.
Pull the plugs the cylinder leaking should have a white coated plug. I would have the head pressure tested at a machine shop before installing a new gasket. Also check for a crack between the cylinder. As it is some work to replace a gasket this is for your protection not that you have a cracked head or block.

Dont worry, you didnt blow a headgasket. Well, at least thats not the reason why your car is overheating. If you ran it long enough with it overheating, a cracked headgasket could result.

However, you just blew the waterpump. This is very common for the V6 duratec. Its even under the contour.org FAQs. The "how-to" to replace it is under the How-to's in the FAQs too.

http://www.contour.org/FAQ/FAQ.php?s=probs&displayid=9