What’s the Best Differential Fluid?

Today’s vehicles produce more power and torque than ever. So, what's the best differential fluid?

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AMSOIL Synthetic Gear Oil
by Joel Youngman
November 18, 2021

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? And, what’s the best gear oil for towing?

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.

Best differential fluid

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.

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.

AMSOIL SEVERE GEAR® Synthetic Gear Lube

AMSOIL SEVERE GEAR Synthetic Gear Lube excels in protecting gears and bearings from the rigors of severe-service operation.

By design, it resists breakdown from high heat, helping to prevent acids and carbon/varnish formation. Its wax-free construction also improves cold-flow properties, improving fuel economy and cold-weather performance.

Superior film strength
Controls thermal runaway
Protects against rust and corrosion
Helps reduce operating temperatures
Maximum efficiency
Long oil, seal and equipment life
Flexible easy-pack for clean, fast installation

We think it’s the best differential fluid available and the best gear oil for towing, but don’t take our word for it. Here’s what some of our customers say:

“Should’ve done this change as soon as I got my vehicle. Now at 250,000 miles on my 2003 Silverado, it is still a big improvement.”

– Javier, Verified Buyer from Duncanville, Texas

“This has been in my race car for several years and the gears show no signs of wear.”

– Bruce, Verified Buyer from Michigan

“The product is worth it just for how easy it is to fill up your differential and, not to mention, it’s the best differential oil on the market, hands down. My actuator in my K1500 front differential engages faster, I believe now, for 4×4.”

– Ryan, Verified Buyer from North Carolina

The best differential fluid should be easy to use

As Ryan alludes to above, SEVERE GEAR is available in the award-winning AMSOIL easy-pack. Its flexible design makes performing tricky gear-lube changes easier, faster and cleaner. No more busted knuckles, annoying gear-lube pump and rigid bottles that waste half the fluid.

If you’re looking for the best differential fluid, give AMSOIL SEVERE GEAR Synthetic Gear Lube a try; we think you won’t be disappointed.


by Joel Youngman

AMSOIL Lead Technical Writer for more than two decades.

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AMSOIL Synthetic Gear Oil

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