Re: drained & filled radiator wrong?
Most thermostats have a bleed hole or sort of a V slot. On a SBF 302/ 289 /351W style engine the bleed should be installed veticaly at the top of the hsg.
Unless you vacuum fill the engine or install a bleeder valve into the top of the water pump impeller cavity its never going to fill the water pump completely.
Signs of it not filling completely are water lines, similar to a bath tub ring, in the water pump impeller cavity, on the cover plate or timing chain cover (if is the style with no cover plate). Pock markes on cover plates which is caused by cavitation DUE TO AIR TRAPPED.
Purchase priemium thermostats I have had issues with the cheeper versions.