Compare the size of the impellers on the two water pumps- - - -if the one you swapped for is noticeably smaller in diameter, you're probably not circulating the coolant fast enough, or there's not enough centrifugal force developed by the impeller to move the coolant through the system.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!