A differential is a set of gears that allows a vehicle’s driven wheels to revolve at different speeds when going around corners or over rough terrain. Those gears require lubrication, which is commonly called differential fluid, gear oil, or gear lube.
How often you should change differential fluid depends on your vehicle, driving conditions and fluid quality. If you drive primarily on the highway in temperate conditions and rarely tow or haul, you won’t need to change the differential fluid very often.
However, severe operating conditions break down differential fluid more quickly and place greater stress on the gears and bearings, inviting wear that reduces their lifespan.
Greater capacity, less lubrication.
Truck manufacturer’s ongoing arms race for the highest towing capacity has resulted in trucks that place more stress on differentials than their predecessors. Meanwhile, differential fluid capacities have largely decreased or remained the same.
For example, compare a 1996 Ford F-250* Crew Cab to the 2021 version. Back in 1996, maximum towing capacity was 10,500 lbs. using a rear differential that held 3.75 quarts of gear oil. The 2021 model offers up to 15,200-lb. towing capacity using a rear differential that holds between 3.3 and 3.5 quarts of fluid.
This means less lubrication is responsible for protecting gears against increased heat and stress. In this environment, inferior lubricants can shear and permanently lose viscosity. Once sheared, the fluid film weakens, ruptures and allows metal-to-metal contact, eventually causing gear and bearing failure.
As temperatures rise, lubricants lose viscosity and the extreme pressure between gears can shear the lubricant film, causing increased metal-to-metal contact, friction and heat. Friction and heat create a vicious cycle known as thermal runaway that spirals upward, leading to increased wear and potential gear failure.
If you tow a trailer or haul heavy loads frequently, especially in warmer temperatures, most manufacturers recommend changing the differential fluid more often, sometimes as often as every 30,000 miles. This applies to most work trucks and anyone who pulls a camper, boat or trailer regularly
The best way to determine the recommended mileage interval for differential fluid changes is to check your owner’s manual. Use a high-quality synthetic gear oil to reduce gear wear and maximize your vehicle’s ability to tow and haul.
AMSOIL SEVERE GEAR Synthetic Gear Lube is specifically designed for severe service. It maintains viscosity better than other gear lubes under rigorous use and contains advanced anti-wear additives for additional protection.
SEVERE GEAR often costs less than OEM-branded gear oil, and the AMSOIL Easy-Pack eliminates the frustrations of changing gear oil. Its flexible design lets you easily reach inconvenient fill holes and squeeze all the gear lube out of the package. Less mess, less waste, less frustration.
AMSOIL Technical Writer and 20-year veteran of the motorcycle industry. Enjoys tearing things apart to figure out how they work. If it can’t be repaired, it’s not worth owning.