Two kinds of thermotropic liquid crystals (5CB and MBBA) are used to study the director nonlinear waves induced by flow in a homeotropic nematic cell. The flow is induced by an exciter, a piece of moving mylar film at one end of the cell. Wave velocities for various exciter velocities and temperatures are measured. A "phase" diagram with our experimental results is constructed and compared with theoretical prediction of reentrant solitons. Waves generated in a first nematic region are observed to be able to penetrate an isotropic region and reappear in a second nematic region.