  In this paper the thermal evolution of scalar field dark matter particles at
finite cosmological temperatures is studied. Starting with a real scalar field
in a thermal bath and using the one loop quantum corrections potential, we
rewrite Klein-Gordon's (KG) equation in its hydrodynamical representation and
study the phase transition of this scalar field due to a Z_2 symmetry breaking
of its potential. A very general version of a nonlinear Schr\"odinger equation
is obtained. When introducing Madelung's representation, the continuity and
momentum equations for a non-ideal SFDM fluid are formulated, and the
cosmological scenario with the SFDM described in analogy to an imperfect fluid
is then considered where dissipative contributions are obtained in a natural
way.Additional terms appear compared to those obtained in the classical version
commonly used to describe the \LambdaCDM model, i.e., the ideal fluid. The
equations and parameters that characterize the physical properties of the
system such as its energy, momentum and viscous flow are related to the
temperature of the system, scale factor, Hubble's expansion parameter and the
matter energy density. Finally, some details on how galaxy halos and smaller
structures might be able to form by condensation of this SF are given.
