did you happen to notice if the bypass is open?
some aftermarket pumps just leave the casting solid. here's my Weiand flat face, notice the roundish opening in the gasket but no hole in the pump body. with no bypass circuit you need to make other arrangements to relieve deadhead pressure until the T-stat opens, and you're free to run a generic T-stat also
there'll be phantoms, there'll be fires on the road... and the white man dancing