Check the hose from the fire wall coming from your heater core you have two hoses one connects to the top of the manifold its just next to the distributor.This one is known to fail it has a very Cheap connection if you can remove it you need to replace it with the old fashion heater hose nipple connector type it`s 3/4" x 1/2 npt it`s 13/4" long. (Auto Zone part no. 56360) then just use a regular 3/4" hose. the heater core is 3/4" size outlet. I replaced my after my wife lost just about all the water dropping the kids at school. please don`t use the original type,I was advised by the Chevy dealer on that.