Pull the T-stat and run the garden hose into the uppermost water inlet of the motor. Water should run out of every hose and passage you got open. If not you got calcium or scale buildup in a water jacket or hose nipple. Maybe put garden hose to heater hose and see if you can get water to flow out of water pump opening, or other opening in water jacket. That'll make sure that there isn't a blockage at heater hose nipple in block. You'd be surprised what rust/scale/lime/calcium buildup will do even with the tasty green fido killer. (antifreeze)
Next pull both upper and lower rad hoses and stick hose into upper rad hose inlet. Water should flow freely from bottom of radiator.
Check business end of water pump and inside all hoses and rad for deposit buildup or other clues to what could be going on. Don't know about this car, but have seen others that use a section of metal pipe between engine water jacket and heater core. It can contain valving or other parts you may not be able to see readily. They also rust.
good luck
chip
