Accurate measurement of engine oil properties is key to ensuring optimum performance and durability. In this study, effective microorganisms (EM) and silver-based additives were used as eco-friendly alternatives to traditional toxic biocides to reduce degradation and microbial contamination of marine engine oils (Marinol). Advanced measurement techniques were used to assess the effect of four types of additives – silver solution, colloidal nanosilver, liquid EM and EM in ceramic tubes – added at a concentration of 2 %. Key oil parameters were measured, including viscosity, oxidation, nitration levels, degradation of anti-wear additives and total base number (analysed by FTIR spectroscopy) and microbial. The results of the measurements showed that the silver solution and ceramic EMs were particularly effective: silver reduced bacterial counts by up to 40 times and ceramic EMs reduced fungal levels by up to 65 times compared to oil without additives. Importantly, the viscosity of the oil with these additives (15.98 mm2/s for the silver and 16.02 mm2/s for the ceramic EMs) was comparable to or better than in the control oil, confirming their practical suitability. The silver solution also showed the highest alkali number (13.18 mg KOH/g), indicating increased resistance to acidic degradation products. One of the key areas for further research is the development and optimisation of the presented integrated approach for use in real-time monitoring systems and field diagnostics. Another important issue will be the implementation of comprehensive data processing algorithms enabling automatic detection of degradation trends and prediction of time to failure. The results of this research may directly contribute to the development of advanced, continuous monitoring systems for marine engines.