## 4 Conclusions  
The lubricating oil in marine engines works in harsh conditions. These depend on factors such as operating load and its changes, fuel quality, ambient temperature, and how the engine is used. The rate at which the oil degrades is heavily influenced by these combined factors. To prevent engine failure, it is crucial to change the oil before it loses its ability to protect the engine. However, frequent, unnecessary oil changes can be wasteful for both environmental and economic reasons. This research investigated the impact of fuel oil dilution on lubricating oil within a marine fuel injection pump through laboratory testing. Based on the experimental results, the key findings are the following:  
* Due to the dilution of oil with fuel, the viscosity index decreased significantly up to 50% for 32 oil operating hours but it remained at a very high or high level (according to ISO grades) for most of the samples. Only oil that worked for 32 h reached the VI medium level. * The increasing amount of fuel oil in the base lubricating oil reduced the antiwear and antifriction performance by decreasing viscosity to 16% at 50 \({}^{\circ}\)C and 29% at 100 \({}^{\circ}\)C if compared to fresh oil. * At the same time, there is no visible effect of diluting the oil with fuel, even on the load seizure limit, where the average value of approximately 3600 N does not change with the amount of fuel in the oil (Figure 10). * To ensure proper reliability of the lubricating properties of the oil, it is necessary to determine the optimal oil change interval. This can be achieved by closely monitoring the actual physical-chemical condition of the oil. * The condition of the fuel injection pump significantly impacts the rate of degradation of the lubricating oil. * In this specific case, due to the observation of lubricating oil being diluted by fuel, it is strictly recommended to adjust the oil change intervals from the manufacturer's recommendation of 100 h to a more frequent schedule (e.g., every 24 h or less). * Alternatively, the oil could be replaced with the one of higher viscosity. However, this could require a re-examination of the oil properties. * Because the design of this pump is a special solution used currently in marine engines, the results of these tests cannot be applied directly to all marine engines. However, the general conclusions will apply to any situation in which the lubricating oil is diluted with fuel. Figure 11: Limit seizure pressure of the tested oil. * (9) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON], [PERSON]; [PERSON]; [PERSON]; [PERSON] Effect of Gasoline-Bioethanol Blends on the Properties and Lubrication Characteristics of Commercial Engine Oil. _RSC Adv._**2017**, \(7\), 15005-15019. [CrossRef]
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