Gear friction, oil churning and bearing losses turn into heat, which leaves through the housing surface. In a worm gearbox, sliding friction between worm and wheel produces more loss; especially at high ratios it is expected to run hotter than a helical gearbox of the same power. This guide gives no general temperature limit; the permissible value is in the gearbox catalogue.

Causes that increase heating:

  • a gearbox selected with too low a service factor or overloaded,
  • too little or too much oil, wrong viscosity, a fill that does not suit the mounting position,
  • a strained bearing, excessive radial load, an overtightened belt or chain,
  • a housing covered in dust, an enclosed space without airflow, direct sunlight.

Practical monitoring: on a new installation, measure housing temperature at the same point over several days and note it; compare later readings with that value. If the motor is also getting hot, the problem may be on the load side; the motor's own heating causes are covered in the motor maintenance and overheating questions guide.