It is known from the experimental studies that the thermal capacities of fluids increase with the use of nanoscale particles in base fluids. Using these fluids in engine cooling systems affects engine performance positively. However, it is not known exactly how the use of these fluids affects other parameters in engines. In this study, the effects on engine oil temperature values were investigated of cooling with nano-fluid support in the internal combustion engine cooling system. As cooling liquid, an ethylene glycol-water mixture (base fluid), which is suitable for use in all seasonal conditions and is widely used, has been used in equal ratio. The effects of the refrigerants prepared by mixing different nanofluids (TiO_2, Al₂O₃ and SiO₂) in different volumetric ratios (0.1% and 0.2%) into the base fluid has been experimentally observed. In the study, a real vehicle engine with an engine volume of 1400 cm³ and operated at an average of 2000 rpm has been used. The increase in heat transfer provided using nanofluid has enabled to remain the engine oil temperature at lower values. It has been observed that the engine lubricating oil can work between 1.5% and 5% cooler. The highest performance was determined as approximately 5% with SiO₂. In general, the increase in the volumetric ratio of the nanofluid in the base fluid has allowed to increase the amount of heat transfer and to remain lower of the oil temperature.