  The Teff location of Pre-Main Sequence (PMS) evolutionary tracks depends on
the treatment of over-adiabaticity. We present here the PMS evolutionary tracks
computed by using the mixing length theory of convection (MLT) in which the
alpha_MLT=l/H_p parameter calibration is based on 2D--hydrodynamical models
(Ludwig et al. 1999). These MLT--\alpha^2D stellar models and tracks are very
similar to those computed with non--grey ATLAS9 atmospheric boundary conditions
and Full Spectrum of Turbulence (FST) convection model both in the atmosphere
and in the interior. The comparison of the new tracks with the location on the
HR diagram of pre--MS binariesis not completely satisfactory, as some binary
components are located at too low \teff. Besides, the pre--MS lithium depletion
in the MLT--\alpha^2D tracks is still much larger than that expected from the
observations of lithium in young open clusters. This result is similar to that
of FST models. Thus, in spite of the fact that 2D RHD models should provide a
better convection description than any local model, their introduction is not
sufficient to reconcile theory and observations. Lithium depletion in young
clusters points towards a convection efficiency which, in pre--MS, should be
smaller than in the MS. The pre--MS lithium depletion decreases significantly
in FST models if we reduce the solar metallicity down to the value suggested by
Asplund et al.(2004), but the corresponding solar model does not reproduce the
depth of the convective zone as determined by helioseismology.
