I purchased my car w/92k miles. At first I had no heat. My mech topped off the fluid from the in/out pipes from heater core, heat returned. That was Dec of 07. inthe summer of 08 the car overheated, i let it cool off, then the car was fine under 50mph. i got home, topped off, car was fine again. 1 mo later, car started overheating again, diagnosed with a bad water pump. Changed radiator, water pump, timing belt, tensioner and put in red fluid. car overheated in shop for 1 week till they finally swapped out the radiator, overheating stopped. When i started driving, the car would ping and clang, clank like a house radiator, it stopped everything was fine, the mech chalked it up to a blockage in the heater core. Its now Jan 09, I have no heat again. i had radiator, hoses, heater core, and expansion tank professionally blown out, still no heat.The radiator tech said lower hose of radiator is cold, likely due to defective water pump! Had mech check again, lines in/out of heater core are hot, Thermostat good, water circulating, but when he dropped the dash, top of heater core is hot, bottom is cold! All of the air ducts work fine, i have a trouble code that reads, major vacuum leak, please help! before i change heater core and water pump at great expense, is it possibly anything else? i have changed the entire cooling system except for the heater core. I'm so desperate, I,ll even accept phone calls if need be. Thanx in advance! Conrad