The thermal convection of modulated viscoelastic flow is examined in this study. The modulation is assumed to be weak enough for a regular perturbation solution to be implemented. In addition to being more accurate, the second-order perturbation results reveal new physical phenomena that could not be predicted by the first-order analysis. Inertia was found to enhance globally the discrepancies between the first- and the second-order perturbation solution. A comparison between the Newtonian and the non-Newtonian solution is carried out and the influences of inertia, modulation amplitude, and wave number are emphasized. The present results show that elasticity has a marked effect on fluid patterns, especially regarding the roll structure and symmetry. The influence of elasticity is greater for larger Rayleigh number and aspect ratio.