A substantial amount of fuel energy is used to overcome internal friction of an engine. Power loss in piston ring-pack accounts for a major portion of this energy loss. Circumferential clearances caused by distorted bores alter the tribological behavior of the piston ring–liner (PRL) interface. This change in performance of the interface intensifies during warm-up of an engine. Mixed-hydrodynamic lubrication model is considered to evaluate the development of tribo-characteristics in piston ring-pack contact with a non-circular liner during the warm-up phase of a spark ignition (SI) engine. Variations in modes of energy loss caused by bore-distortion during the warm-up period are analyzed. Oil transport to the combustion chamber throughout the warm-up process is studied. Five different viscosity-grades are considered to compare performance of the interface. Results show that viscous shearing of lubricant oil is largely responsible for frictional loss in the warm-up phase. Circumferential variation in film thickness decrease parasitic losses in cold temperatures, but increases oil transport both in cold and in warm conditions.