We consider the full system of compressible Navier-Stokes equations for
heat conducting fluid. We show that the temperature is uniformly
positive for $t\geq t_0$ (for any $t_0>0$) for any solutions with
finite initial entropy. The assumptions on the viscosity and
conductivity coefficients are minimal (for instance, the global in time
solutions constructed by E. Feireisl verify all the requirements).