  MXB 1659-298 is a transient neutron star Low-Mass X-ray binary system that
shows eclipses with a periodicity of 7.1 hr. The source went to outburst in
August 2015 after 14 years of quiescence. We investigate the orbital properties
of this source with a baseline of 40 years obtained combining the eight eclipse
arrival times present in literature with 51 eclipse arrival times collected
during the last two outbursts. A quadratic ephemeris does not fit the delays
associated with the eclipse arrival times and the addition of a sinusoidal term
with a period of $2.31 \pm 0.02$ yr is required. We infer a binary orbital
period of $P=7.1161099(3)$ hr and an orbital period derivative of
$\dot{P}=-8.5(1.2) \times 10^{-12}$ s s$^{-1}$. We show that the large orbital
period derivative can be explained with a highly non conservative mass transfer
scenario in which more than 98\% of the mass provided by the companion star
leaves the binary system. We predict an orbital period derivative value of
$\dot{P}=-6(3) \times 10^{-12}$ s s$^{-1}$ and constrain the companion star
mass between $\sim$0.3 and $ 0.9 \pm 0.3$ M$_{\odot}$. Assuming that the
companion star is in thermal equilibrium the periodic modulation can be due to
either a gravitational quadrupole coupling due to variations of the oblateness
of the companion star or with the presence of a third body of mass M$_3 >21 $
Jovian masses.
