you can take off both heater hoses, off the alt bracket, take a garden hose to either hose, it dont matter, and flush the core, you should get the same flow out as what is going into the core from the hose. a nice medium flow works well, you dont want to get yourself soaked.

its possible that the core is air locked as well. so when you finish flushing it out, keep both hoses as full of water as you can and put them back on.

then bleed the coolant system.