Investigating an operational Diesel engine from Mercedes regarding the fuel consumption and emissions level to define a mathematical model constitutes the main objective of the study. Evaluation of pollutant emissions represents a global concern. The specific objectives of the study consist in experimental measurements, data collection, processing, digital modelling and comparative analyse of two operational scenarios regarding the coolant temperature evolution. Thermal conditions are strongly influencing the fuel consumption and the pollutant emissions. The proper results of present scientific effort are consisting in optimal applied models for defining engine operational parameters.