Both reductions with oil could be attributed to a simple dilution effect. During the 2 h hot oil treatment, the temperature of the oil ranged from 86 C to 90 C (measured at t ¼ 0 and 120 min, respectively). Heat was applied to the system through a steam-jacketed insulated main tank. Circulatory piping was not heated. Therefore, the oil in portions of the equipment that were not heated and/or insulated may have been at a lower temperature than oil in the heated tank.