Updated at: 20-07-2022 - By: Lucas

Gear oil and lubricants are essential in the workings of a vehicle. They prevent corrosion, oxidation, and rust from forming on the car’s components. There would be more damage to the components, especially the gear system, if there are no oils and greases in the system.

However, because to differences in viscosity and other properties, not all oils are suitable for use in specific automobile components. Viscous oil provides better protection than thin because of its constancy in thickness.

Transmission oil is essential to the smooth operation of transmission units, which operate at high speeds, pressures, and temperatures.

To ensure optimal starting characteristics and long-term performance, transmission oil must have the appropriate viscosity properties. What is the ideal viscosity of the oil?

In addition, because it thickens so much at lower and moderate temperatures, its viscosity can have an effect on the efficiency of your car’s gears.

The protection and efficiency that high-quality oil can provide your car’s gear are now evident. Which 75w90 or 80w90 gear oil is best for your vehicle? Wait and see.

But before we get into the specifics, keep in mind that the manufacturer’s recommendations should always be followed when selecting gear oil with viscosities of 75w90 or 80w90.

With their knowledge of how the transmission works, they can recommend the appropriate fluid for your car. It’s also quite practical, since a lubricant producer is unlikely to pass up the chance to add tolerances from technical firms on the bottle label… (as most do).

75w90 gear oil

75w90 vs 80w90 (3)

Limited slip differentials and cold regions benefit from the usage of 75W 90 transmission oil, which is formulated for extreme pressure situations.

Heavy-duty manual transmissions, final drives, and axles benefit from this oil’s ability to withstand high temperatures.

This is a high-performance, anti-friction-treated gear oil that can be used for a variety of applications. SAE class is denoted by the 75w90. The oil’s flowability at low temperatures is denoted by the W symbol.

The W indicates that the oil is still flowable at temperatures as high as 40 degrees celsius, which is equivalent to 40 degrees Fahrenheit. The kinematic viscosity of this oil at 100 degrees Celsius is 90.

Viscosity index

The viscosity index of 75W 90 gear oil is 144.

Temperature range

With its tough and steady qualities, the oil is perfectly suited to all of the vehicle’s driving needs. It is resistant to oxidation and heat impacts. Cold-weather and high-pressure applications benefit the most from the usage of this lubricant.

Gear oil with a 75W90 viscosity rating should be used when the ambient temperature is between 148.8°C and 176.6°C.

Kinematic viscosity

At 40 degrees Celsius, the oil’s kinematic viscosity is 115.


At 210 degrees Celsius or 410 degrees Fahrenheit, this oil’s flashpoint is.

80w90 gear oil

75w90 vs 80w90 (2)

Extreme pressure applications and non-synchronized manual transmission lubrication in huge vehicles or buses can both benefit from 80W 90 gear oil. Differentials with limited slip or conventional clutches should use this gear oil.

The viscosity classes of the oil are indicated by the 80 W 90 numerals. There are two grades of viscosity and two numbers on this gear oil. In this oil, the W indicates for the oil’s winter stability.

This oil’s designation as having a workability index of 80 indicates that it performs admirably even at subfreezing conditions. The oil’s thickness at 100 degrees Celsius is represented by the second value, 90.

Even at temperatures as low as 14°F (26°C), the oil can flow. At a temperature of 100 degrees Celsius, oil has a kinematic viscosity of 90.

As a result, the kinematic viscosity of this fluid might range from 13.5 to 18.4 square millimeters per second. Heavy loads are no problem for the oil, which has excellent shear stability.

Viscosity index

The viscosity index of this oil is 90.


80W 90 gear oil has a flashpoint of 222 degrees celsius, or 431. 6 degrees Fahrenheit.

Temperature range

Suitable for both high and low temperatures, this oil is versatile. Summer and winter are included. This oil can be used in temperatures ranging from 13 degrees Fahrenheit to 95 degrees Celsius.

Differences between 75w90 vs. 80w90 gear oils

  • 80W 90 gear oil is denser than the 75 W 90 gear oil.
  • Due to its thinness, 75w 90 gear oil offers better gear protection than its thicker counterpart. Therefore deemed to be good overall.
  • 75W90 gear oil has a consistent viscosity and thickness across a wide range of temperatures.

Advantages of 75w90

  • Excellent resistance to foaming
  • Grants longer seal life
  • Has a good film strength maintenance which enhances reliable lubrication

Pros 80w90 gear oil

  • Has high thermal stability
  • Offer excellent protection against rust and corrosion
  • Has a high load-carrying capability

Similarities between them

  • Both oils have almost similar flashpoint, pour point, and fire point temperatures.
  • Both are safe for use with open differentials, manual transmissions, and limited-slip differential in heavy-duty trucks.
  • They both can protect against wear, rust, and corrosion.
  • Both are ideal for heavy city use and can handle extreme pressure.

Can I mix 75w90 instead of 80w90?

Even though these oils can be mixed, it is best to consult your car’s owner’s handbook before doing so. The mechanic should also be consulted before any mixing takes place.


Modern additive systems are used in the synthetic oil 75W90 and 80W90 formulations. Based on their characteristics, these oils can be used in a variety of ways.

Extreme temperature applications benefit most from 75W90 gear oil. Cold temperatures and limited slip differentials are ideal applications for this product.

Non-synchronized manual transmissions in heavy-duty vehicles can benefit from 80W90 oil. Suitable for limited-slip and conventional gearboxes.