The possibility of using ultrasound energy to reduce the viscosity of frozen diesel fuel in long 3D-curved channels of small diameter was demonstrated experimentally. The effectiveness of the proposed method is due to the thermal effect of ultrasound and intensification of mixing of the liquid fuel with solid wax particles on the phase boundary under the effect of elastic vibrations. The ultrasound effect does not alter the properties of diesel fuel regulated by GOST 305-82. For this reason, the proposed method can be used in automotive and tractor engineering.