When a gearbox runs hot sometimes the first port of call is to change the crude based oil with synthetic gear oil. But; Will synthetic gear oil decrease operating temperature?

Although additives can improve
many qualities of crude based oils, it is not possible to exert an unlimited influence on all their attributes. This pertains especially to the following physical properties:

• thermal resistance
• low temperature attributes (fluidity, pour point)
• flash point
• evaporation loss

Synthetic gear oils have the following advantages:

• improved thermal and oxidation resistance
• enhanced viscosity-temperature response, high viscosity index (in most cases)
• enhanced low temperature attributes
• reduced evaporation losses
• reduced flammability (in some cases)
• improved lubricity (in some cases)
• lower tendency to form residues
• improved resistance to ambient media

At precisely what temperature do I need synthetic gear oil

Most of the time, you begin to detect the extra life provided by a PAO synthetic gear oil above 160 degrees F. If it is above 180 degrees F, and especially 200 degrees F, the difference in oxidative life becomes quite obvious.

However there’s no single temperature point that dictates a time to move to synthetic gear lubricants. The determination is dependent on equipment, continuous loads and shock loads, equipment availability for routine maintenance, criticality of the application, component life cycles, lubricant life cycles and failure modes; amongst other things.

Generally, the rate of lubricant degradation doubles with every 18 degrees F increase in oil temperature. Once formulated with antioxidant additives, PAO-based lubricants have a lower baseline rate of oxidative degradation. At low temperatures, a PAO's increased oxidative life may not be noticeable, particularly if you have to change the oil at some point for other reasons. At higher temperatures, the synthetic may last noticeably longer.

However it’s not only temperature that dictates whether you need synthetic gear oil

The point at which a change to synthetic is justified is dependent perhaps on a handful of additional "program management" parameters such as:

• Does the machine's operating temperature vary a great deal (a PAO's high viscosity index enables it to operate across a wider temperature range)?
• Do you mean to run your gear oils with a suitable use of filtration and oil analysis to allow life-cycle extensions?
• Are you currently doing oil analysis and undertaking condition-based changes?
• Do you have, oxidation limits that flag impending oxidation issues?
• Do you have an effective contamination control program in place that will enable you to fully exploit the PAO's extended life?

Aside from the fact that synthetic gear oil can decrease operating temperature; with the suitable management strategy, a change to a high-performance synthetic lubricant can actually cost considerably less than the comparable mineral oil product type.

Outside of these factors, somewhere around 165 degrees F presents the point at which you possibly should begin to ponder the use of synthetics for the sake of lubricant longevity, if not for the sake of reliability.

To conclude whether synthetic gear oil can decrease operating temperature:

Yes Synthetic gear oil can decrease operating temperature, but the added benefits of reduced friction, energy saving, and reduced operating costs through reduced maintenance, longer oil change intervals and less wear really make the use of synthetic gear lubricants a no-brainer.