It isn't at all crazy to size the new motors based upon the current drawn by the old motors. The current on the old motors is a very rough measure of the torque loading the old motors. So if you make the presumption that the old motors were simply mechanically overloaded, then going to new motors of the same output shaft speed but higher torque capability is probably a good solution.
However the _evidence_ is that after the motors were increased in capacity, they were _still_ overloaded. Togol, I totally agree with you; this strongly suggests some serious other problem.
'Power factor' cannot directly be an issue here. The motors will consume current that is slightly out of phase with the applied voltage, but external factors cannot change the _internal_ power factor of the motor. As long as the voltages at the motor terminals are correct and _balanced_ the over-all power factor on the feeder to the motor is not relevant.
Can you confirm that the motors were replaced 'like for like', eg. a 4 pole 1800 RPM motors with larger 4 pole 1800 RPM motors? Are the motors of similar class with similar slip versus load characteristics.
Were any shaft speed measurements taken on the old and new motors? What I am wondering is if there is some strange interaction between the pressure regulation, the pumps, and the motors, such that the motors _never_ get up to speed. The motors could be happily running along in a high slip, low efficiency condition, burning themselves up. Note that if the problem is the motors not actually getting up to speed, then a larger motor might be able to push past the 'hump' and function correctly, but this is not the real fix to the problem.
-Jon
