The ornamental design for a grille for radiator, as shown and described.
FIG. 1 is a front perspective view of a grille for radiator showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is an opposite side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
It will be understood that the broken lines shown in the drawings illustrate portions of the grille for radiator that form no part of the claimed design.