Throughout the Figures, where shown: (i) the dashed lines showing additional structure of the marine outboard engine cowling side panel are for illustrative purposes only and form no part of the claimed design; (ii) the unshaded surfaces form no part of the claimed design; and (iii) the dotted/dashed lines illustrate unclaimed boundaries of surfaces claimed as part of the design. A second embodiment of the invention includes the mirror image of the embodiment of the marine outboard engine cowling side panel shown in the Figures.