This paper presents an experimental and statistical study of a four-cylinder turbocharged compression ignition engine operating in dual-fuel mode with natural gas and liquid pilot fuel (diesel or hydrotreated vegetable oil). The main engine performance indicators, combustion process parameters and emissions were evaluated, as well as noise and vibration measurements were performed to determine the loading of structural elements. In order to highlight the factors affecting engine reliability and maintenance, the ANCOVA (analysis of covariance) methodology was applied, modeling the influence of load, natural gas fraction and sound pressure. The mean absolute percentage error shows that the model predicts the most important indicators quite accurately under various operating conditions. The developed ANCOVA model not only predicts engine characteristics under various load and fuel mixture conditions, but it also provides insights useful for engine maintenance planning and reliability assurance, especially in long-term or intensive operation.