I'm getting almost no heat out of the heating system even at normal engine temp.

What is your question?

My S40 heater puts out almost no warm air even though the engine is at normal temp. All the heater fans work, the gates all operate properly so the only thing the mechanic can figure is that the core is plugged and needs replacing. At $500 for the core and $800 for labor, that's a chunk of dough! Will flushing open up the core, or is there a heater thermostate or valve that could be the problem?