I recently replaced a Pentair WhisperFlo 1.5hp WFE-6 (Model 011514) single speed, circa 2000, with a Pentair WhisperFlo 1.5/0.19hp WFDS-6 (Model 011512) two speed.
One very noticeable difference between the two pumps is how much hotter the WFDS-6 motor runs. Higher case temperature (touching the outside of the case) as well as the noticeably warmer fan exhaust temperature. I haven't used a temperature gun on it, but subjectively it is a hotter motor.
Heat loss is a form of inefficiency. I notice the older motor was marked AO Smith "E-Plus" whereas the new motor is an AO Smith but without the "E-Plus" designator.
Any ideas on why a newer motor (running on the same circuit) runs so much warmer? I checked voltage at the motor and it is a healthy 240V +/-.