The differential in an automobile is a gear box that essentially allows different wheels to turn at various rates. Because the differential contains a variety of moving parts in the form of gears, it is essential to properly lubricate the parts to allow proper function and prevent damage. Differential oil is specifically designed for this purpose.
Differential oil, or gear oil, for all intents and purposes is a type of motor oil. What sets differential oil apart from normal engine oil is that it is specifically formulated to provide proper lubrication for the gears in the differential of a car, truck or sport utility vehicle. Differential oil is primarily different from engine oil in that it is thicker or more viscous. A higher viscosity means that the oil will not only penetrate the inner workings, or gears, of the differential; it will stick to and coat the gears.
Differential gear oil is broken into classifications by the American Petroleum Institute. One important point is that motor oil and differential oil ratings are not comparable and should not be interchanged for each other. Differential oils are typically heavier and more viscous, and are not suited for engines. Likewise, engine oils are not designed to lubricate the heavy gears of a differential.
Ranging from a rating of GL-1 to GL-6, each rating is tied to a specific type of operating condition. For example, GL-1 is a more basic oil designed for light operating conditions and specific types of differential gear setups. At the opposite end of the spectrum is API GL-6, which is designed for very heavy conditions and extreme shocks and abusive conditions.
As with any vehicle fluid, it will be necessary to periodically replace the differential fluid at recommended intervals. Vehicle manufacturers will specify the proper interval and type of oil to be used. However, this is probably the most commonly overlooked service with regard to personal and work vehicles. Especially in the case of off-road and four-wheel, full- and part-time vehicles, it is vitally important to adhere to a regular routine of maintenance of your vehicle's differential.
Additionally, it is important to consider the lubrication requirements of your vehicle's limited slip differential. Sometimes referred to as traction sensing, this feature is designed to detect when a wheel loses traction and transfers more power to the wheel that has traction in order to compensate. This feature places special demands on the differential, and the correct oil is essential to ensure the proper workings of the limited slip feature.
Don't second-guess the engineers who designed your vehicle's parts. Extensive time was spent on the design of the differential for your vehicle, and the recommended oil is not a suggestion. Only use the oil that is recommended for your vehicle's differential. Failure to do so could result in damage to the internal gears, a time-consuming and expensive repair. Strictly follow the manufacturer's guidelines in this case to ensure your vehicle's differential performs properly.
