1992 Mazda MX6 with 2.2 liter 4 cylinder, manual transmission, AC, 275,000 miles that just recently started to overheat but recovers on its own (temp goes up while driving on highway at 70 mph and then goes back to normal, flat road (Dallas to San Antonio)) so looking for possible causes.

How often have you folks seen a water pump quit pumping (shaft comes loose from pulley or impeller)? I've never changed one that wasn't leaking so not sure how often this happens. The last pump I installed had a cast iron impeller like I used to see back in the 70's (kind of a cast iron disc with curved vanes cast into it). The impellers of the original and next 2 pumps were kind of sheet metal with tabs bent up making paddles (kind of if you know what I mean).

Also, will a blocked heater core cause this motor
to overheat?