Short answer
Identify the exact front or rear axle and differential type, then use its specified gear-oil viscosity, performance requirement, capacity, and additive instructions. Front and rear axles on the same vehicle can require different products or quantities. Limited-slip additives are application-specific.
Identify each axle separately
Record the axle identification or equipment code, whether you are servicing the front or rear, and whether the differential is open, limited-slip, or locking. A towing or off-road package may change the axle fitted to a vehicle with the same model name.
Make a separate entry for each compartment on your shopping list. Do not copy the rear-axle quantity into the front-axle row or assume that changing one services both. Confirm whether an AWD assembly also has a separately serviced clutch or coupling.
Match viscosity and the required specification
Record both the gear-oil grade, such as the one listed in your manual, and its performance specification or manufacturer fluid requirement. Different axle designs can call for different viscosity grades. A higher number is not automatically a better substitute.
API GL categories describe application requirements; they are not a simple ladder that makes every higher number a replacement for a lower one. Keep differential oil selection separate from manual-transmission and transfer-case selection.
Source: AMSOIL transmission and gear-oil reference.
Check limited-slip additive instructions
Some clutch-type limited-slip differentials need specified friction characteristics. Follow the axle manufacturer’s additive requirement and quantity together with the chosen oil’s guidance. An electronic locker or a gear-type limited-slip unit should not automatically be treated like a clutch-type unit.
AMSOIL states that its synthetic gear lubricants are generally limited-slip capable without extra modifier, while certain applications may still need it. Do not add a tube by default or use an additive to mask a mechanical fault. Confirm the exact axle requirement first.
Source: AMSOIL: what a limited-slip additive does.
Plan the service quantity and hardware
Check the prescribed service capacity and final fill-level method. Depending on the axle, the job may involve a drain plug or removal and resealing of a cover. Identify the required gasket or sealant, seal washers, torque values, and curing instructions before starting.
Confirm that the fill point can be accessed and opened before draining. Have the correct pump or dispensing arrangement, enough fluid, a drain container, and safe access to the vehicle. Use the specified final level, which is not universally the bottom of the fill hole.
Source: AMSOIL component application lookup.
Use the schedule and inspect unusual findings
Consult the axle maintenance schedule for towing, heavy loading, or other severe use. Water exposure or suspected contamination warrants the manufacturer’s inspection guidance rather than waiting for the next routine interval.
Record which axle was serviced, its fluid code, quantity, additive if used, date, and mileage. Persistent chatter, leaks, or abnormal debris calls for diagnosis. Shop compatible gear oils only after the axle specification is confirmed.
Sources checked . Prices and product guidance may change.
Frequently asked questions
Do front and rear differentials use the same oil?
Sometimes, but not always. Verify each axle’s viscosity, specification, additive requirement, and capacity separately.
Does every limited-slip differential need an extra additive?
No. Requirements depend on the differential design and the selected lubricant. Follow both the axle and product instructions.
Is differential fluid the same as transfer-case fluid?
Do not assume so. They serve separate components that can require different lubricants and service procedures.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].
