The invention relates to a cooling-channel piston for an internal combustion engine, having an upper part and a lower part, wherein the upper part and the lower part are connected to one another by way of a cohesive joint in the form of a weld seam, and the upper part and the lower part form an annularly encircling cooling channel which is arranged approximately behind a ring section, wherein a gap geometry is provided between a lower edge of the ring section and an upper edge of the lower part, wherein the gap geometry has at least one sliding surface which is arranged on a lower edge of the ring section of the cooling-channel piston and/or on the corresponding upper edge of the lower part of the cooling-channel piston, and to several methods for the operation of a cooling-channel piston.