  The angle dependence at different temperatures of the longitudinal thermal
conductivity $\kappa_{xx}(\theta)$ in the presence of a planar magnetic field
is presented. In order to study the influence of the gap symmetry on the
thermal transport angular scans were measured up to a few Kelvin below the
critical temperature $T_c$. We found that the four-fold oscillation of
$\kappa_{xx}(\theta)$ vanishes at $T > 20 $K and transforms into a one-fold
oscillation with maximum conductivity for a field of 8 T applied parallel to
the heat current. Nevertheless, the results indicate that the d-wave pairing
symmetry is the main pairing symmetry of the order parameter up to $T_c$.
Numerical results of the thermal conductivity using an Andreev reflection model
for the scattering of quasiparticles by supercurrents under the assumption of
d-wave symmetry provide a semiquantitative description of the overall results.
