## 4 Results and Discussion
The flash point was similar to new oil without additives. The remaining samples achieve results in a similar range of approximately 200 \({}^{\circ}\)C, which disqualifies them; due to safety reasons, the flash point should have the highest possible value. Figure 6: Coloring of new oil, with the addition of silver solution (SS) and colloidal nanosilver (CN) in liquid form. Figure 7: Flash point for oil with effective microorganisms (EM), colloidal nanosilver (CN), and silver solution (SS). Statistical analysis was performed for a significance level of 95%. The obtained results for the water content and the flash point for the new oil and the new oil with additives for this significance level do not show any significant errors, because they fall within the lower and upper confidence intervals. In order to confirm the obtained results, the article also presents a graph of viscosity versus temperature (Figure 8). In this diagram we can see that the curve of viscosity versus temperature for oil with the ceramic tubes is very similar to the curve for new oil without additives. On the other hand, the highest viscosity, which differs significantly from the viscosity of the oil without any additives, is of the oil with 2.5 mL of EM. Viscosity is 720 mPa-s at approximately 2 \({}^{\circ}\)C, which is similar to that of used oil 6, for which the viscosity at this temperature is 719 mPa-s. Other additives, including silver compounds, also increase the viscosity of the oil, but not as much as liquid effective microorganisms. Although effective microorganisms contain molasses, which is rich in sugar, no adverse effects on the rheology of the engine oil have been observed. At this stage, the dynamic viscosity was measured with a vibration viscometer. The obtained results demonstrate that the addition of ceramic effective microorganisms is more effective in new oil, whereas their liquid form is more effective in used oil. This should be confirmed by future research, and the effect of additives on the elemental composition of the oil and investigation into whether rheological shear thinning is evident are other potential areas of research. These tests will check whether molasses has a negative effect on the performance of the engine oil. Figure 9 shows the water content in used oil (additives were added after using the oil). The chart compares the water content of oil without additives with that of oil that has been mixed with effective microorganisms and silver compounds. For a better illustration, the graph also shows the result for new oil. From this figure, we can see that for used oil the water content is approximately 0.17%, while for liquid microorganisms in a quantity of 2.5 mL, this amount is 0.6%, and for 5 mL, the result was not obtained due to over-titration, as was the case with new oil. This means that the water content was above the measuring range. As for new oil, the situation was different for microorganisms in a ceramic tube form. The water content for three ceramic tubes was about 0.02%, for six tubes it was 0.05%, while for new oil the water content was 0.09%. The addition of silver, regardless its type and  
Figure 8: Viscosity for oil samples with the addition of effective microorganisms (EM), colloidal nanosilver (CN), and silver solution (SS). amount, is also not possible to present on the graph due to over-titration, i.e., the amount of water with these additives was above 1%. Similarly to new oil, in this case the lowest water content was obtained with the addition of EMs in the form of ceramic tubes, in a smaller quantity. Previous research [55; 56; 57] also shows that better parameters for used oil are obtained by adding EMs in liquid form. An example is the flash point shown in Figure 9. Moreover, Tables 2-5 show a comparison between the parameters of fresh and used oil without additives, and those in which the additives of effective microorganisms and silver compounds were added.