Selecting Gear Lube for Your Engine Parts

Gear lube is the type of motor oil used for transmissions, differentials, and transfer cases in trucks, automobiles, and other heavy equipment in order to prevent metal-to-metal contact that can cause severe damage. It has a higher viscosity, or thickness, than regular motor oil. This helps the lubricant to move through the moving parts when there are no pumps present to push it through the system, which is the case with much of the heavier equipment.

After viscosity, it is important to consider which type of gear lube you need. There are many different types, but most fall into these three broad categories:

Rust and Oxidation Inhibited (R&O).

This type does not include antiscuff additives or other agents, but it does a good job of preventing corrosion and excess foam. It is designed for moving parts that operate at high speeds but with low, consistent loads. It is not intended for use in engines that are prone to spikes in activity.


This is also known as an extreme pressure (EP) lubricant, and it performs far better than R&O oils. The antiscuff lubricants contain special additives that make them stronger and able to carry larger loads. One of these common antiwear additives is sulfur phosphorous, which works to alter the machine surface to prevent the adhesive in boundary lubricants from wearing away. Other additives include molybdenum-disulfide (moly), graphite, and borates. An advantage to these additives, compared to sulfur phosphorous compounds, is that their activation does not depend on high surface temperatures. However, sulfur phosphorus additives can eventually harm machine surfaces, especially yellow metals. Engines that perform well with antiscuff gear lube are those that operate under heavy loads or at slow speeds, as well as those that have regular spikes in activity.


This type of lube is mixed with a synthetic fatty acid to increase its strength and lubricity. It is commonly used in worm gear applications, where the gears move in a regular sliding motion and are built from metals that may corroded if antiscuff lubricants are used. Compound lubricant is also known as cylinder oil, since it was originally used for steam cylinder machinery.

Finally, you will want to choose a base oil that’s suited to your particular equipment and application.

Mineral Base Oils: This type is suitable for most uses. It allows for greater film thickness in certain applications. However, the inherent properties of this type make it unsuitable for many high-temperature applications. After the refinement process, many inorganic compounds remain. Three in particular-oxygen, sulfur, and nitrogen-can allow oxidation, acid development, and sludge formation.

Synthetic Oils: This type is an engineered product designed to generate a chemical reaction based on the machine’s pressure and temperature. The high-purity chemical components have strong molecular bonds, so they are less likely to break down or allow oxidation. These strong bonds also keep the lube from getting too thick when it’s cold or too thin when it’s hot. They generally offer more consistent protection in sliding applications.

When considering the type of gear lube for your vehicle or heavy equipment, the owner’s manual is the first place to find the recommended viscosity, type, and base oil. Alternatively, a service professional should be able to recommend something for your machine, based on the type of equipment and your use. Having the right lubricant is essential to keeping your machines running efficiently and effectively for many years.