Electric vehicles (EVs) continue to replace internal combustion engines (ICEs) in the automotive marketplace to counter environmental impact and rising fuel costs. EV lubricants possess unique properties and have requirements that were not demanded in standard ICE transmission applications. These fluids are entering the industry at a rapid pace and are not yet fully characterized. In this study, rheological properties of an EV fluid were measured and implemented into a line-contact elastohydrodynamic lubrication (EHL) model. EHL simulations were conducted over a range of automotive operating conditions. A two-part closed-form regression was established for viscous and asperity contact regimes to estimate local friction due to instantaneous contact conditions. Validation of the friction formulae was performed by measuring spur gear power loss in a modified ISO-standard four-square test machine. In this arrangement, total power loss is the sum of load-dependent and load-independent losses of two identical gearboxes. Gear mechanical power loss was estimated by removing unloaded gearbox power loss and bearing mechanical power loss. Measurements covered various inlet temperatures, speeds, torques, and surface finish qualities. Super-finishing achieved great success in power loss reduction. Super-finishing one or both gears dropped mechanical power loss by 10 and 15%, respectively. Experimental results matched predictions quantitatively, particularly when considering the rough surfaces. The methodology successfully implemented rheological properties of an EV fluid and applied it to automotive gear contacts. Mechanical power losses for spur and helical gear contacts can be estimated under any operating conditions, given conditions lie within the simulated EHL test matrix.