This study experimentally investigates the scarcely studied stratified, oil-based sensible thermal energy storage (STES) tank, to examine the heat retention capability of Hytherm-600 silicone oil during the standalone period and its heat dispatchability during the discharging process. To conduct an experimental study on the thermic oil, a vertical cylindrical tank with a helical discharging coil fitted inside is used. Three different oil charging temperatures (50, 70, and 90 °C), and three different discharging flow rates (water) through the helical coil (0.5, 1.25, and 2 L/min) have been considered. The thermal stratification phenomena in oil and the evolution of thermocline have been investigated. Results indicate the formation of a thermocline zone of 154 mm thickness in the lower portion of the tank within 3 h from the commencement of the stand-alone period. The discharging operation fluctuates the thermocline stability in the storage medium (i.e., commercial thermic oil Hytherm-600). During the discharging operation, a water flow rate of 0.5 L/min through the helical coil led to higher discharging efficiencies owing to better heat transfer attributable to the higher water residence time inside the coil. For the aforesaid water flow rate, the average discharging efficiencies are 85.6%, 75.6%, and 81.6% for the charging temperatures of 50, 70, and 90 °C, respectively. Finally, the primary thermocline thickness is found to be constant at 82 mm following the splitting of the initial thermocline during the discharging operation.