  We prove that there exists a~large-data and global-in-time weak solution to
a~system of partial differential equations describing an unsteady flow of an
incompressible heat-conducting rate-type viscoelastic stress-diffusive fluid
filling up a~mechanically and thermally isolated container of any dimension. To
overcome the~principle difficulties connected with ill-posedness of
the~diffusive Oldroyd-B model in three dimensions, we assume that the~fluid
admits a~strengthened dissipation mechanism, at least for excessive elastic
deformations. All the~relevant material coefficients are allowed to depend
continuously on the~temperature, whose evolution is captured by
a~thermodynamically consistent equation. In fact, the~studied model is derived
from scratch using only the~balance equations for linear momentum and energy,
the~formulation of the~second law of thermodynamics and the~constitutive
equation for the~internal energy. The~latter is assumed to be a~linear function
of temperature, which simplifies the~model. The~concept of our weak solution
incorporates both the~temperature and entropy inequalities, and also the~local
balance of total energy provided that the~pressure function exists.
