In this study, the production process for lithium-based Grease using treated waste engine oil as the base oil was investigated. Waste engine oil was collected and purified by settling, filtration, thermal dewatering, acid treatment, neutralization, and post-treatment filtration to ensure suitability for grease production. Grease compositions were developed using Minitab’s Extreme Vertex Mix Design software, varying the proportions of treated engine oil, lithium hydroxide (LiOH), Graphite, and calcium carbonate. Fourteen formulations were prepared, and samples were tested according to ASTM standards for dropping point, oil separation, evaporation loss, and copper corrosion resistance. The best formulation was determined to be 81.66% treated base Oil, 11.67% LiOH, and 6.67% additives, which delivered superior thermal performance. Findings revealed that LiOH content was directly correlated with thermal stability, and that both LiOH and the additive contributed to reduced oil separation and evaporation loss. Mixing temperature also affected stability, with 160°C yielding better structural integrity than 200°C. All samples maintained low evaporation loss across temperature variations. The study demonstrates that recycled waste engine oil can serve as a reliable, cost-effective, and environmentally friendly raw material for grease production, contributing to circular economy goals and offering a viable solution for industrial-scale manufacturing.