Transmission oils: classification and characteristics

Transmission oils are a special class of engine oils intended for use in different friction points of vehicle transmissions, as well as in various gearboxes. Motor and transmission oils are produced on a mineral or synthetic basis, and then alloyed with a variety of additives, but the requirements for transmission are higher, since they work at much higher loads and sliding speeds of friction surfaces. One of the most important indicators of such oils is the ability to create a protective film on the surface of friction units to prevent mechanical contact between them. In hypoid gears, oils are used that, when reacting chemically with the surfaces of parts, prevent them from skipping, have anti-seize properties. During operation, the transmission oils oxidize and become contaminated, so they must be periodically changed. Good oil is considered to be oil with a low tendency to oxidation. Since different manufacturers use different additives, their products can not be mixed. When replacing the transmission unit, it must be thoroughly rinsed, if possible with the same fresh oil.

Classify transmission oils, either by viscosity or by performance. So according to SAE (Automobile Engineers Association) they are divided into nine classes - five summer and four winter (with index W). For each class, the viscosity index is indicated. SAE 70W or SAE 250, for example. For multigrade oils, a double index is indicated (SAE 80W-90, etc.).

API (American Petroleum Institute) divides the oils into 6 classes depending on the operational properties - GL-1 ... GL-6. These classes are similar to those used in the Soviet GOST 17479.2-85 TM1 ... TM6. The fifth and sixth groups are used for hypoid gears and have the highest lubricating and extreme pressure characteristics.

When choosing gear oils, you should focus on the conditions of their work. If the class is lower than necessary, the mechanism will simply fail, and a higher grade of oil will have a higher cost, which will lead to a cost overrun. It is also important to consider at what temperatures the transmission will work, and proceeding from this to select the lubricant. SAE 85W, for example, will operate at temperatures down to -12 ° C, and 85W already up to -40 ° C. In automatic transmissions a special low-viscosity liquid is used, therefore neither motor nor transmission oil is used there.

Today in the market a large range of manufacturers offer their transmission oils - Lukoil, Total, Texaco, Rexol, Norsi and many others. The variety of additives used determines both the level of quality of oils, and their price range. Mineral, usually, is cheaper, but it serves less, synthetics are exactly the opposite. A good compromise in this case will be semisynthetics, as the golden mean between the first two. You should also beware of fakes and do not buy oil in unchecked stores. Changing the box is always more expensive than taking a good, quality oil, especially since now they are nursed from 60 thousand or more kilometers from replacement to replacement.