This study represents performance tests of the third-order turbulence closure for predictions of separating and recirculating flows in a backward-facing step. Computations of the momentum and temperature fields in the flow domain being considered entail the solution of the time-averaged transport equations containing the secondorder turbulent fluctuating products. Formulations have been made for the triple products, which are responsible for the diffusive transport of the second-order products, by developing each corresponding transport equation. A low Reynolds number model associated with the viscous effect in near-wall regions is developed and incorporated in the computation. The computations are compared with several algebraic models and with the experimental data in literature. The prediction has been improved considerably, particularly in the separated shear layer.