  The collision dynamics of $^{17}O_2(^3\Sigma_g^-) +^{17}O_2(^3\Sigma_g^-)$ in
the presence of a magnetic field is studied within the close-coupling formalism
in the range between 10 nK and 50 mK. A recent global {\em ab initio} potential
energy surface (PES) is employed and its effect on the dynamics is analyzed and
compared with previous calculations where an experimentally derived PES was
used [New J. Phys {\bf 11}, 055021 (2009)]. In contrast to the results using
the older PES, magnetic field dependence of the low-field-seeking state in the
ultracold regime is characterized by quite a large background scattering
length, $a_{bg}$, and, in addition, cross sections exhibit broad and pronounced
Feshbach resonances. The marked resonance structure is somewhat surprising
considering the influence of inelastic scattering, but it can be explained by
resorting to the analytical van der Waals theory, where the short range
amplitude of the entrance channel wave function is enhanced by the large
$a_{bg}$. This strong sensitivity to the short range of the {\em ab initio} PES
persists up to relatively high energies (10 mK). After this study and despite
quantitative predictions are very difficult, it can be concluded that the ratio
between elastic and spin relaxation scattering is generally small, except for
magnetic fields which are either low or close to an asymmetric Fano-type
resonance. Some general trends found here, such as a large density of
quasibound states and a propensity towards large scattering lengths, could be
also characteristic of other anisotropic molecule-molecule systems.
