O.K. I replaced the waterpump but I didn't change the thermo. So now for some reason the thermo is sticking and overheating the engine. What interests me in this is that the pump I took out had exposed fins (no flat disk) in the pump vortex area whereas the jobber pump I put in had the usual looking flat disk that I presume is in front of the fins. None the less the thermo eventually opens and the temp goes back to normal.
So was my old pump a higher output design that was masking a failing thermo? Or am I just a cheap bastard who saved a few pennies when he had a perfect opportunity to change the thermo in a well lit heated garage and who is now going to pay for his miserly behavior by changing a thermo in a windchill of -40?