“Can synthetic lubricants help reduce heat in gear drives? I've heard that they will, but I'm not sure if it justifies the higher price.”
There are many performance and economic reasons to change to a higher-priced lubricant for gear drives. Heat is the critical factor from a mechanical perspective.
As the heat goes up in the gearbox, the viscosity thins. As the viscosity thins, there is an increase of boundary conditions (metal-to-metal contact), which generates more heat. The frictional heat serves to further thin the lubricant, causing a circular decay in the effectiveness of the lubricant.
Synthetics generally have higher viscosity indices (VIs). This serves to resist the problems associated with hot drives. Synthetics have been used to effectively reduce the operating temperature of gear drives by 10 to 50 degrees F.