I never had one of those thermometers, in fact they probably hadn’t even been invented yet when I was doing this for a living, So I can’t comment too much on your readings. But I will say that the only ones I find surprising are 5 & 6. On the other hand, you are running in a can at unknown speed and time and with air bubbles mixed with the water So I’m not too alarmed — yet. Service the pump and get it on a boat and see what happens. And try not to worry so much.
The motor hasn’t been used in salt water has it? Or has it?