In this research, a diesel engine lubricant, modified with Multi-Walled Carbon Nanotubes (MWCNTs) was evaluated. Carboxylic group functionalized MWCNTs were dispersed in 15W40 mineral oil for Diesel engines and retaining ring and cylinder sleeve materials from F300 diesel engine were used for tribological tests. The Nanofluid (0.1 0.5 and 1% wt.) rheological behavior was characterized. Nanolubricants with 1% wt and base oil were evaluated on a Pin-on-Disk test. Results suggest both wear rate and coefficient of friction reduction when MWCNTs are used, while no significant rheological properties changes were observed.