Choosing the right ISO viscosity grade for enclosed gearboxes

Selecting an ISO viscosity grade is one of the most consequential decisions in gearbox specification — too thin, and the oil film breaks down under load; too thick, and churning losses waste energy and generate excess heat.

Start with the manufacturer's plate

Most gearbox nameplates specify a recommended ISO VG range. When that's unavailable, operating temperature and pitch-line velocity become the deciding factors — higher speeds generally call for lower viscosities to reduce churning losses, while heavier, slower loads need the film strength of a higher grade.

“A gear oil one grade too thin fails faster than one grade too thick — when in doubt, round up.”

Matching RBM GearMax grades

RBM GearMax is available from ISO VG 68 through VG 460, each formulated with extreme-pressure additives rated for FZG load stage 12 or higher — suitable for worm drives, enclosed spur and helical gearboxes, and heavy conveyor transmissions.

Our technical team can review your gearbox specification sheet and recommend an exact grade — reach out through the contact page for a same-day response.