A comprehensive analysis of engine performance and fuel consumption was carried out to study Low Heat Rejection (LHR) concepts in the conventional light-duty diesel engine. From most previous studies on LHR diesel engines, thermal-barrier coatings (TBCs) have been recognized as a conventional way of insulating engine parts; while for the cases studied in this paper, the LHR concept is realized by altering engine coolant temperature (ECT). This paper presents engine simulation of a multi-cylinder, four-stroke, 1.9L diesel engine operating at 1500 rpm with five cases having different ECTs. The simulated results have been validated against experimental data. Calibration strategy for the engine simulation model is detailed in a systematic methodology for a better understanding of this simulation-development process. The calibrated model predicts the performance and fuel consumption within tolerated uncertainties. Simulated volumetric efficiency and residual gas fraction (RGF) are in agreement with the experimental data and empirical RGF prediction model, respectively. The results indicate that increasing ECT yields improved fuel conversion efficiency, which is likely due to decreased heat rejection to the coolant. The observed variation trend of the fuel conversion efficiency is generally consistent with the existing literature on LHR engines. Because of the technical difficulties in operating a conventional production engine at higher coolant temperatures (> 120°C), the validated model can be further applied to study operating events with expanded ECTs (albeit, in extrapolation). It is noted that results shown in this paper are demonstrated for low-load case to support continued development of combining LHR with low temperature combustion; a full-scale study of LHR concept needs to be further studied at higher engine loads.