Here we investigate through the use of 2 and 3D spherical shell models, the effect of temperature, stress and depth-dependent viscosity on surface mobility and the rate of core heating. The influence of a depth-dependent viscosity on surface mobility is explored by considering the viscosity contrast occuring accross the 670km depth phase boundary. Additionally, we look at the stress- dependent effects of plastic yielding on the mobility of the surface with the use of a depth-dependent yield stress. The planetary bodies to be modeled feature an Earth-like core size relative to planetary radius and a combination of basal heating and internal heating.