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. (c) 2016 Elsevier Ltd. All rights reserved.