i had the same thing happen to me . i put a new impeller kit in a alpha 1 . it ran and pump water on the muffs . when in the lake the thermostat gauge climbed pass where i knew something wasn't right ,back to trailer it went before overheat . when i took the water pump apart again found i used a wrong gasket witch closed off half a two part water port . once the right gasket was installed all was fine . the impeller kit came with multiply gaskets for different applications