Mini and micro-scale channels have drawn researchers' attention in the past three decades. The use of these tiny channels in a heat exchanger is considered as one of the pioneered works on the narrow channels as minichannels provide high heat transfer rates per unit volume. Motor oil, known as engine oil, is one of the vital fluids in automotive applications. Its cooling process is confronted by its thermo-physical properties, especially viscosity, which makes this process difficult.In current investigations, experimental endeavors have been performed using a closed loop thermal wind tunnel to verify the aptness of cooling the motor oil through a cross-flow minichannel heat exchanger. The prototype heat exchanger consists of 3 circuits; each circuit has five slabs which are connected to each other by four serpentines. There are 68 channels of 1 mm circular diameter drilled through each slab. The minichannel heat exchanger comprises of wavy fins arranged parallel to the flow of air. The inlet temperature of the motor oil was kept constant at 75°C while the air inlet temperatures were varied within the range of 20°C and 40°C.The flow of the oil fell in the laminar regime due to its high viscosity, which consequently resulted in low Reynolds numbers (Re). The range of was found to be from 0.85 to 3.5 whereas the air flow rates were between 6 m/s and 18 m/s. Correlations were developed between the oil Nusselt number and oil Re and Prandtl numbers. The effect of Re on the heat transfer coefficient, NTU, and effectiveness were investigated. The results were compared with the findings of another highly viscous fluid where a similar test specimen was used and same trends were observed.