| Summary: | <span>Iraqi petroleum refineries produce large quantities of base lubricating oils (lube oils). Managing the influence of nano-additives on the lube oil nanofluids is required deep understanding to explain the resulting new specifications of produced nano-lubricants. The present study investigated the effect of Al<sub>2</sub>O<sub>3</sub> NPs addition on the thermal properties of lube oil stock-60. Different mass additions of 0.25, 0.65, 1.05, 1.45, and 1.85 wt.% of Al<sub>2</sub>O<sub>3</sub> NPs at operating temperatures of 20-50°C were evaluated. Also, the thermal conductivity coefficient of the prepared nanofluid was studied at the full range of the experimental temperatures (20-50°C). It was noted that the addition of Al<sub>2</sub>O<sub>3</sub> NPs improved the thermal properties of the prepared nano-lubricant due to the high thermal conductivity of the added Al<sub>2</sub>O<sub>3 </sub>NPs. Moreover, the greatest improvement in the thermal conductivity of modified nano-lubricating oil was 13.02% at added Al<sub>2</sub>O<sub>3</sub> mass fraction of 1.85%. The results indicated that the viscosity index of the prepared nano-lubricant was improved dramatically with Al<sub>2</sub>O<sub>3</sub> NPs addition increase at measured standard temperatures of 40 and 100°C. The viscosity index of lubricant nanofluid is increased up to 2.46% at a weight fraction of 1.85%. The flashpoint increased by 1.33, 3.54, 5.75, 7.52, and 9.73% for mass fraction of 0.25, 0.65, 1.05, 1.45, and 1.85 wt.%, respectively. Furthermore, the highest flashpoint value was 248<sup>o</sup>C of prepared nanofluid lube oil with 1.85 wt.% of Al<sub>2</sub>O<sub>3</sub> NPs. Finally, the produced nano-lubricating oil has high operating quality with economic feasibility. Furthermore, an accurate correlation for predicting the viscosity of both types of nano-lubricants was provided.</span>
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