Oldsmobile/Buick Repair: No Heat/leaking coolant, coolant leak, air conditioner evaporator


Question
My 91 old calais with a 2.5 has not had heat for the last month almost.  I replaced the thermostat twice and I just noticed that there is a coolant leak.  it looks like it is coming from the area around the bottom of the water pump.  The "weep" hole on the water pump is dry though.  Also like one of your previous questions, there has been a "swooshing/bubbling" sound that must be coolant.  It would be very appreciated if you could respond with your best answer for this crappy problem.           thank you

Answer
Hi Scott,
I would feel the need to find out if coolant is being pushed through the heater core.
The best way to be sure of that is find out which heater hose goes from the pressure side of the pump, and then remove the other hose, and start the car, and see if coolant is flowing. It should flow even with the thermostat closed, and cool. You can catch the coolant, or pump it right back into the radiator, but I would want to see it flow.
Once I am sure it is flowing, I want to make sure the heater hoses get hotm meaning hot coolant is flowing.
If that is happening, then there is a door in the heater assembly that is not allowing the airflow to pass through the heater core, but it is passing through the air conditioner evaporator, which is cold when the defroster is turned on, in order to remove the moist air from the airflow.
As for the leak, as long as the engine and heater core are full of coolant, the heater should work. But I would search a little closer to see where it is coming from.
Van