What is the specific gravity of the liquid. High specific gravity consumes more motor kilowatts. Viscous products consume more power also. They also cause the pump to operate off the best efficiency point causing shaft deflection problems. The seal face load is very important.
Wide faces generate more heat.
The axial thrust of the shaft can increase the face load. The installation skill of the mechanic is critical. Because they are mounted outside the stuffing box thermal growth of the shaft can increase the face load in most non-metallic designs. The shaft speed is a major factor. The faster you go the more heat generated.