What’s the Best Differential Fluid?

Posted On: Nov 18, 2021 8:11 AM

Today’s vehicles produce substantially more horsepower, torque and towing capacity than their predecessors, yet the design of differential gears and bearings remains largely unchanged. Many differentials even use less gear lube and lower viscosities than before in an effort to reduce drag and increase fuel economy. In essence, less gear lube is responsible for providing more protection. So, what’s the best differential fluid for the job?

Fighting the grind

Differential designs have inherent weaknesses.

In a traditional automotive differential, the pinion gear concentrates intense pressure on the ring gear. As the gear teeth mesh, they slide against one another, separated only by a thin layer of lubricant.

The repeated stress the lubricant film bears can shear gear lubes, causing permanent viscosity loss. Once sheared, the fluid film weakens, ruptures and allows metal-to-metal contact, eventually leading to gear and bearing failure. Severe-service applications, like towing, amplify the situation.

Thermal runaway

The extreme pressures and temperatures placed on gear lubricants can lead to a serious issue called thermal runaway.

As temperatures in the differential climb, some gear lubes lose viscosity and load-carrying capacity. When extreme loads break the lubricant film, metal-to-metal contact occurs, increasing friction and heat. This increased friction and heat, in turn, results in further viscosity loss, which further increases friction and heat.

As heat continues to spiral upward, viscosity continues to spiral downward. Thermal runaway is a vicious cycle that leads to equipment damage from extreme wear and, ultimately, catastrophic gear and bearing failure.

Original Source: https://blog.amsoil.com/whats-the-best-differential-fluid/