New 3/4 HP motor overheats

[jimlongIII]

Hi all and thank you in advance for any help. I replaced my 10 year old motor with a new 3/4 hp after it started squealing. The new A O Smith motor will run for approx. 20-30 min. and shut off. Actually this is my 2nd motor as I thought maybe something was wrong with the first one. The 2nd motor does the same thing, gets hot (around 180-190 F) and the safety mechanism inside the motor shuts it off. I've replaced the shaft seals, had the impeller/diffuser examined and all is as it should be. I checked the voltage at the timer and motor and am receiving 240v. The motor is switched to 230v inside the motor cover as this is a 220V system. I'm just beating my head against the wall trying to figure this out, any and all help would certainly be appreciated. Jim