The eruptions of Old Tardy look similar to those of Tardy Geyser but the craters look different. Old Tardy is a fountain-type geyser. Intervals range from minutes to hours, durations range from seconds to hours, though a few minutes is more the norm. The maximum height is 10-15 feet.
The water level in Old Tardy follows the same rises and falls as the rest of the Sawmill Complex.