A general field transformation for transient three-dimensional multicomponent energy and species equations is presented. Employing this transformation, transient multicomponent transport coupling effects in three-dimensional hows with surface injection cooling are studied. A new multicomponent transport coupling parameter is introduced and new results for the surface heat flux for various values (between 0 and I) of this parameter are given. These values of the transport coupling parameter represent a wide range of transport properties of multicomponent mixtures. The present results demonstrate how a given final surface cooling efficiency can be obtained by choosing a variety of combinations of various values of the transport coupling parameter and injection rates. The present study also reveals an interesting behavior of local overshoot values in the transient relative contribution of the transport coupling effects to the surface heat flux. This behavior is explained here in terms of fluctuations in a multicomponent ’Transport-coupling Activity’ number, which is sensitive to the differences in the characteristic rate of change of the local concentration gradients with respect to the local temperature gradient.