Thanks for the input. The plot thickens a bit. I removed the tank and blew air into the pipe. Did not sense any resistance or hear anything break loose, but air was flowing up out of the t-stat housing opening - so that pipe seems to be open. The radiator hose is attached, so this was the only open exit. Next step, I guess, is to first see if water will (hopefully) now flow for some reason and, if not, seal up the T-stat and see if air makes it to the front. Fingers crossed.
But this will have to wait until after the Ohio State - Penn State game!
Ron