A considerable slide exists between the flanks of worm and gear during the work, which results in flank wear and considerable loss of energy. The energy is, thereby, converted into heat, which leads to the warming-up of gear drive, compromising its correct operation, and to scuffing in critical cases. Oil temperature has an important role in thermal stability. Viscosity depends on temperature. Viscosity significantly affects the processes in the contact zone, i.e. the energy losses, and hence the temperature. Optimal lubrication can be provided only in the relevant field of temperatures. The paper presents experimental and theoretical research on the effect of temperatures and thermal stability of a worm and gear set with a gear made of sintered steel Fe1.5Cr0.2Mo on their ability and appearance of boundary conditions.