Condenser fan motor overheats and then shuts off
Is this condenser fan motor for a split system with the condensing unit  outside? Can you check the running amperage of the new motor to make sure it is not running in an overloaded state? Are you sure that the new motor is the same H.P. as the old motor? Did you check the old and new motors to make sure that the input voltage and RPM  are the same? There has to be a good reason for the new motor to overheat.