OOOOOOOOOOOOOOOOOOOOoooooooooooooooh, a Sable! Why didn't you say so? I had the plastic water pump impeller disintegrate on mine; caused overheating, percolating sounds from the heater, and coolant loss with NO cooling system leaks. Check water pump output and if none REPLACE!
http://ecomodder.com/forum/165952-post11.html