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75w85 Vs. 75w90: Which One Is Better?

Selecting a gear oil is an important consideration for your vehicle when it comes to maintenance and ensuring it functions smoothly and efficiently. Gear oil companies continue to develop new formulations to keep up with the performance demands of modern vehicles while also focusing on quality.

Two main competitors in the gear oil circuit are 75w85 and 75w90. Each oil is a high-quality lubricant that comes with its own set of benefits and features, but if you’re looking for a complete comparison, you’re in the right place.

Take a look at what are the differences between the two oils and find out which one is better for your vehicle.

How Are The Motor Oils Named?

The naming convention for gear oils includes a classification made by the Society of Automotive Engineers (SAE). The SAE class for 75w85 and 75w90 are made of two components. The numeric value before the letter W stands which stands for winter suitability, corresponds to a temperature value that indicates maximum flowability of the liquid at colder temperatures.

75w means that the liquid will remain flowable until it reaches the temperature of -40 degrees Celsius. The numbers after the W, which in this case are 85 or 90, refer to the viscosity of the oil when it reaches a temperature of 100 degrees Celsius, with the 90 variants being more viscous than the 85 ones.

How Do The 75w85 And 75w90 Differ?


As we mentioned previously, the numbers at the end represent the kinematic viscosity of the oil, but why is it important to know about viscosity?

When winter arrives, it leads to the gears becoming choked up, which can become a problem, especially when temperatures go below 0 degrees Celsius. At such low temperatures, the engine might stop functioning, or it might lead to a significant decrease in functioning. In such conditions, lubricants are required to counteract the friction in the gears, thereby allowing them to function smoothly.

The gear oils used need to be accounted for when it comes to the viscosity, as if the fluid has a higher viscosity index, it takes longer to flow and coat the surface of the gears in the car. For effective use during the winter season, the oil needs to be thick, and you have multiple options available, including the 75w90 and the 75w85, with the 90 being thicker and more viscous than the alternative. 


Additives are used in gear oils to enhance their functioning and resolve issues that can arise in the gears of your engine or vehicle. Different formulations have different additives; for example, 75w85 is loaded with anti-rust properties, which prevents the formation of rust in gears. Additionally, the oil is also good at handling pressure due to its additive composition.

When it comes to the 75w90, the additives included in its formulation are responsible for regulating its viscosity at different temperatures, which it’s better at counteracting friction present in the gears while also allowing you to start your engine must faster during winters.

Seasonal Effectiveness

Lubricant oils have a lot of problems during winter. As the temperature drops, the oil thickens. As a result, their fluidity and viscosity are restricted. Low viscosity equals low traction, which can cause the engine gears to stall.

Oils with a 75w90 grade are designed to keep their qualities even in cold conditions. It is also specially developed to adjust to regular temperature fluctuations.

75w85, on the other hand, has comparable characteristics. In a warm atmosphere, it becomes thicker, and in the winter, it becomes thinner. This allows your vehicle to be more flexible throughout the cold months.

Gear Protection

Russia is the enemy of gears which are primarily made of metals that can be easily worn down when they come in contact with water or if they’re exposed to a humid environment.

The 75w85 is not formulated to prevent rust as it was primarily designed to act as a lubricant, and it cannot offer additional protection for rusting. The 75w90, however, is capable of acting as a protective shield against water vapors, and therefore, it is effective at protecting the gears from corrosion and rust.

The formulation comprises certain additives that allow them to provide protection against moisture, and this oil can also be mixed with the 75w85 to further enhance gear performance.

Shear Stability

Shear stability refers to an oil’s capacity to withstand mechanical stresses and the resulting physical degradation caused by tearing and, in certain conditions breaking. The shear stability is also dependent on viscosity as it is affected by the resistance to viscosity changes.   

The thickness of the lubricant you’re using might be affected by shear stability. When selecting an oil for your engine, it would be important to factor in the thickness of the oil, so you can get the optimum results when it comes to the traction of your vehicle.

Additives have an impact on shear strength as well— the viscosity increases as the number of additives increases. Therefore, the shear resistance increases as viscosity increases.

The thickness of 75w85 is considered to be moderate. As a result, the shear stability of 75w85 is much lower. However, through the incorporation of additives, the thickness and shear stability can be enhanced.

75w90 has excellent shear stability, and it has a much higher viscosity than 75w85 due to its additive composition. This further enhances the shear stability of this lubricant as well. 

Final Thoughts

Both the oils have a different set of characteristics and features that make them suitable for different vehicles and machines.

While the 75w90 has certain features such as rust prevention and other additives that make it slightly better than these 75w85, you are free to mix and match these oils or even use one instead of the other as they are pretty close in the formulation.