## 3 Results and Discussion
Particularly, under high-temperature working conditions, the additive helps reduce the influence of temperature on viscosity reduction, contributing to maintaining more stable working conditions compared to the case without the additive. Similarly, for oil B, the viscosity-temperature relationship in both cases with and without the additive is depicted in Figure 5b. The viscosity changes from 139.799 mPa.s to 54.831 mPa.s corresponding to a temperature increase from 25 \({}^{\circ}\)C to 85 \({}^{\circ}\)C. With 0.5% additive, these values change from 148.443 mPa.s to 60.908 mPa.s as the temperature changes from 25 \({}^{\circ}\)C to 85 \({}^{\circ}\)C. Thus, in the case of the additive, the viscosity increases by 6.2% and 11.1% at 25 \({}^{\circ}\)C and 85 \({}^{\circ}\)C, respectively. For oil C, this result is shown in Figure 5c, where the viscosity of the oil increases by 8.1% and 16.6% at 25 \({}^{\circ}\)C and 85 \({}^{\circ}\)C, respectively. Figure 5: Viscosity of oils with and without additive at different temperatures: (**a**) for oil A; (**b**) for oil B; (**c**) for oil C.  
From these results, it can be seen that the fly-ash additive added to the base oil at a 0.5% weight ratio plays an important role in reducing the influence of temperature on viscosity. Moreover, the additive is particularly effective with oil A, increasing the viscosity by 32.8% at 85 \({}^{\circ}\)C. This can be understood as the base oil of oil A having the lowest viscosity among the tested oils. Therefore, when adding an appropriate amount of additive, the lubricating properties of the oil are significantly improved compared to the case without the additive. However, the optimal amount of additive is still under research. In this study, the focus was only on testing with a 0.5% additive ratio. This will serve as a basis for further research to find the most suitable additive ratio, ensuring better lubricating properties than the base oil. Indeed, for oil A, the viscosity increased from 38.365 mPa.s to 47.119 mPa.s, which is approximately a 22.8% increase compared to the case without the additive. In contrast, at this temperature, the viscosity of oil B increased by 10.2% with the additive. In the case of oil C, the viscosity also increased by approximately 11.5% compared to the case of using the base oil. From these results, it can be observed that the additive improves viscosity when operating at 75 \({}^{\circ}\)C, with oil A showing the most significant improvement, followed by oil C and oil B. At different temperatures (40 \({}^{\circ}\)C and 65 \({}^{\circ}\)C), the influence of the additive on the viscosity reduction follows a similar pattern as the results analyzed above. This overall view of the viscosity reduction's dependence on temperature in the presence of the additive at these temperatures can be observed in Table 6 and Figure 5. Therefore, based on the analyzed results, it can be inferred that if the base oil has a higher viscosity, the impact of the additive on enhancing viscosity under different temperature conditions is not as effective as in oils with lower viscosity. The presence of the metal oxide additive can be interpreted as forming a material layer that transforms sliding friction into rolling friction on the surface of the friction pairs. It acts as a medium that enhances the heat dissipation process, thereby reducing the influence of temperature on viscosity. Thus, this study focused on investigating the effects of an additive, specifically fly ash, on the viscosity and load-carrying capacity of three industrial oils (A, B, and C) at different temperatures. The experiments were conducted using a viscometer under realistic operating conditions, and shear stress measurements were recorded for both the oils with and without the additive. The results demonstrated that the shear stress varied with the shear rate for each type of oil, and the changes in shear stress were attributed to variations in the viscosity characteristics of the oils.