75w90 vs 75w140 Synthetic Gear Oil: Which One to Choose?

Synthetic gear oil is crucial in reducing friction and wears between the gears by providing superior lubrication. Thus, it is crucial to choose the right oil for your car. However, it can be a great dilemma when you have to choose one from the two options, such as 75W90 Vs 75W140.

One of the key differences between these two gear oils is their thickness. The 75w90 is thicker compared to the thickness of the 75w140. Each has specific justifications for why it is superior to others when it comes to cost, fuel efficiency, or any other factor.

So, today in this guide, we will explore the differences between these two gear oils to help you choose the one that suits your needs.

Overview of 75w90 Synthetic Gear Oil

The 75W90 synthetic gear oil safeguards the gears in a car’s gearbox and transmission. 

It has exceptional load-carrying performance when severe pressures and shock loads are anticipated and are suited for usage in multiple railway gears.

It has a viscosity rating of 75 at low temperatures and 90 at high temperatures. 

It has various applications, including car trucks and heavy-duty equipment. 75W90 is very useful when you drive in extreme temperatures or under heavy loads.

Good Sides

  • Has better resistance to oxidation, thermal breakdown, and shearing
  • Better than typical mineral-based gear lubricants
  • Can handle extreme pressure 
  • Reduce operating temperatures 


  • The 75w90 is a bit more expensive than regular mineral-based gear oils

Read Also: 75w90 Vs. 75w140: Find The Best Bang For Your Buck

Overview of 75w140 Synthetic Gear Oil

The 75W-140 is a synthetic drivetrain oil designed to fulfill API GL-5 and other stringent quality standards. It has a viscosity of 75 at low and 140 at high temperatures. 

They also have a unique additive package that lengthens bearing life, improves lubricity, and ensures reduced gear sound. 

It is commonly used on off-road vehicles, commercial trucks, and racing cars subject to extreme temperatures and prolonged periods of use.

Good Sides

  • Offers better film strength than mineral oils at extremely high temperatures.
  • It enables efficient lubrication without channeling at subfreezing temperatures.
  • Fewer maintenance costs  
  • Provide superior protection and performance


  • You might require a slip additive

75w90 vs 75w140: Quick Comparison Table

It’s important to note that the specific requirements for gear oil will vary depending on the manufacturer and model of your vehicle. 

So knowing about the differences between these two gear oils can help you find the suitable option. 

Properties75w90 Synthetic Gear Oil75w140 Synthetic Gear Oil
Viscosity 75 at low temperature and 90 at higher temperature75 at low temperature and 140 at higher temperature
Recommended usageDaily maintenance Heavier usage
EP additives lowHigh
Resistance to oxidation, thermal breakdown, and shearingGoodBetter
Fuel EconomyMoreLess
PriceLess expensiveMore expensive

Read Also: Can I Use 5W30 Instead of 5W20? (Helpful Tips and Explanation)

What are the Differences Between 75w90 and 75w140 Synthetic Gear Oil?

By now, you already know the common differences between the 75w90 and 75w140 synthetic gear oil. 

However, a more detailed analysis can help make the right decision more confidently. Keep reading to know more. 


One of the most important factors when buying gear oil is viscosity. It has a big impact on how a lubricant film forms. 

By making the lubricating oil more viscous, a thicker lubrication layer is produced, which enhances the anti-wear, dampening, and scuffing load capacity of the oil.

75W90 has a viscosity rating of 75 at low temperatures and 90 at higher temperatures, while 75W140 has a viscosity rating of 75 at low temperatures and 140 at higher temperatures. 

This means that 75W140 is thicker than 75W90, particularly at higher temperatures.

Recommended Usage

In their respective functions, 75W90 and 75W140 are both acceptable for routine maintenance.

Nevertheless, 75W140 is more frequently used for heavier-duty purposes or heavier usage because of its higher viscosity at higher temperatures. 

The standard uses include use in heavy-duty trucks, off-road vehicles, and towing trucks.

Nevertheless, because 75W90 synthetic gear oil has a lesser viscosity at higher temperatures, it is often advised for use in lighter-duty uses like automobiles, light trucks, and high-performance cars.

Read Also: 5w40 vs 15w40: Which one ensures Longevity, Performance & Value

EP Additives

These gear oils have many additives like friction modifiers, anti-wear, anti-foaming, etc. But, the main difference will be seen in the EP additives. 75W140 has a higher concentration of extreme pressure (EP) additives than 75W90.

In heavy-duty uses where the gears are exposed to substantial pressure and shock loads, 75W140 is a better fit. 

On the other hand, the 75W90 has a lower concentration of extreme pressure (EP) additives, which makes it easier to flow and provides sufficient protection for gears under normal operating conditions.

Resistance to Oxidation, Thermal Breakdown, and Shearing

Due to the composition of the 75w140 gear oil, it has better resistance to oxidation, thermal breakdown, and shearing than 75W90. 

This is because 75W140 contains a greater density of additives to withstand oxidation and thermal breakdown and a higher viscosity that makes it more shear-resistant.

Contrarily, 75W90 gear oil has a lower additive content, which might make it more prone to oxidation, thermal breakdown, and shearing during rigorous operation. 

Although it is still a high-quality gear oil that can offer excellent protection when used commonly, it might not be as effective in heavy-duty situations as 75W140 gear oil.

Read Also: 0w40 vs 5w40: Which Synthetic Oil is Better for Your Car?

Fuel Economy

Fuel economy also greatly influences choosing the right gear oil for your car or truck. Generally, the 75w90 has a better fuel economy than the 75w140.

Since 75w90 has a thinner viscosity, it degrades less under extreme heat. The thinner composition allows for less energy consumption and improved efficiency. 

This may differ, though, depending on the additives and fluid content of the gear oil, as different brands often offer different oil compositions.

Remember that operating conditions also play a role in fuel economy. On the other hand, as 75w140 is designed for usage in extreme conditions and loads, it is often less efficient in fuel economy than 75w90.


You will also see a bit of price difference between 75w90 and 75w140 synthetic gear oil. The 75w90 is less expensive than the 75w140 gear oil due to the composition of these liquids.

75w140 comes with a higher concentration of EP additives and is meant for more heavy-duty usage, making it more expensive than the other option.

75w90 or 75w140: Which Gear Oil to Choose?

The choice between 75W90 and 75W140 synthetic gear oils depends on the specific application and the manufacturer’s recommendations. These gear oils perform excellently, but depending on your application, one is more suitable than the other.

If you operate under heavy loads or extreme conditions, 75W140 synthetic gear oil may be better for superior protection and performance. 

However, if you are operating under normal driving conditions and fuel economy is a concern, 75W90 synthetic gear oil should be sufficient. 

Also, Consider using 75W-90 if you live in cold weather. But, use 75W-140 if you are located in a warm one.

Read Also: 15w40 vs 10w30 Motor Oil Comparison: Know The Difference


After reading our guide, it is common to have some questions so we will discuss all these Faqs below. Keep on reading to have a better idea about our discussion today’s discussion.

Can I use 75w90 and 75w140 interchangeably?

You won’t notice many differences when you switch between these two gear oils. Moreover, when using your car to tow heavy loads, you can consider using 75w140 instead of 75w90.
However, following the manufacturer’s recommendations for the type of gear oil that should be used in your vehicle is essential. 

Can traditional gear oils and synthetic gear oils be combined?

Combining synthetic and conventional gear oils is not advised as it can reduce performance and perhaps harm the gears and other components. The excellent qualities of synthetic oils are diluted or suppressed when combined with regular oils, which might decrease the oil’s efficiency.

How frequently should I change my gear oil?

An oil change for manual transmissions is typically necessary every 30,000 to 50,000 miles. Conversely, automatic gearboxes typically require oil changes every 60,000 to 100,000 miles. Nevertheless, this also relies on the manufacturer’s suggestions and the conditions in which your vehicle is operated.

Is synthetic gear oil better than traditional gear oil?

The increased protection, functionality, and longevity of synthetic gear oil make it frequently preferred over traditional gear oil. Improved oxidation, thermal disintegration, and shear protection from synthetic gear oil will make your transmission and other parts last longer.

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