The balancing act
Transmission components need a lubricating film that separates loaded surfaces while still flowing to gears and bearings at start-up and during operation.
Temperature matters
Viscosity falls as oil gets hotter and rises as it gets colder. The correct grade therefore depends on component design and the operating-temperature envelope.
Do not substitute casually
Changing from an OEM-specified viscosity or fluid family can alter shift feel, friction behaviour or component protection. Always confirm the approved specification before substitution.
This article is general technical information and is not a substitute for the equipment OEM manual, lubricant manufacturer recommendation or site-specific engineering review.