This paper is an investigation of the effects of a thermal bulk fluid in brane world models compactified on AdS5. Our primary purpose is to study how such a fluid changes the bulk dynamics and to compare these effects with those generated by matter localized to the branes. We find an exact cosmological solution for a thermally excited massless bulk field, as well as perturbative solutions with matter on the brane and in the bulk. We then perturb around these solutions to find solutions for a massive bulk mode in the limit where the bulk mass (mB) is small compared to the AdS curvature scale and T < mB. We find that without a stabilizing potential there are no physical solutions for a thermal bulk fluid. We then include a stabilizing potential and calculate the shift in the radion as well as the time dependence of the weak scale as a function of the bulk mass. It is shown that, as opposed to a brane fluid, the bulk fluid contribution to the bulk dynamics is controlled by the bulk mass.