Whats the point of turning on the heater? There is no heater core shut-off in these cars.

If the heater core is plugged or restricked there won't be any, or reduced, heat out of it. The fan on -max- will sustantiate that.

I gotta say, I know of no one who has ever reached into the cabin to feel for heat when purging air out of a cooling system.

I do it every time.

Like bluejay_32 indicates ... It's SOP (Standard Operating Procedure). *old-school.
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Did that a couple years back on a old 2000 buick century replaced head gaskets. Gem of a time the weird procedure on that car purging air. So nice when it finally started throwing heat out of the vents.