Can You Mix 75W90 And 75W140? The Ultimate Guide.

Published by Dustin Babich on

Mixing 75w90 and 75w140 is not recommended. Mixing different viscosity grades can lead to poor performance and damage to your vehicle.

Choosing the right gear oil for your car is essential for its smooth functioning. Gear oil is a lubricant used in manual transmissions, transfer cases, and differentials. It protects the gears from wear and tear, reduces friction, and prevents rust and corrosion.

The numbers in gear oil, such as 75w90, and 75w140 indicate its viscosity grade. Viscosity is the measure of the oil’s resistance to flow at a particular temperature. Mixing different viscosity grades of gear oil can lead to problems in your vehicle’s drivetrain. In this post, we will discuss whether you can mix 75w90 and 75w140 gear oils.

Can You Mix 75W90 And 75W140 Gear Oils?

Mixing gear oils is a topic of interest for many car enthusiasts. If you’re wondering whether it’s possible to mix 75w90 and 75w140 gear oils, the answer is yes. However, it’s not recommended by most manufacturers due to the risk of altering the properties of the oil.

Mixing different types of gear oils may lead to oil breakdown, reduced lubrication, and increased wear and tear on gears. Moreover, it could void any manufacturer warranties. To know if your gear oil has been mixed, check for differences in color or consistency.

Always stick to the manufacturer’s recommended oil type and do not mix unless it’s absolutely necessary.

Understanding The Differences Between 75W90 And 75W140 Gear Oils

Gear oils play an important role in keeping your vehicle’s transmission working properly. They come in different viscosity ratings such as 75w90 and 75w140, each having its own unique composition. 75w90 gear oil is less viscous and contains fewer additives, making it suitable for light-duty vehicles.

On the other hand, 75w140 gear oil is thicker, more durable, and has more additives, which makes it suitable for heavy-duty vehicles. Using the right gear oil for your vehicle can help it perform better and last longer. However, there are also certain advantages and disadvantages to using each type of gear oil that you should consider before making a decision.

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By understanding the differences between 75w90 and 75w140 gear oils, you can make an informed choice on which type is best for your vehicle.

Choosing The Right Gear Oil For Your Vehicle

Gear oil is a vital component in any vehicle’s transmission system. Choosing the right type can greatly affect your vehicle’s performance on the road. Factors to consider include the type of vehicle, driving conditions and climate. It is important to use the recommended gear oil type specified by the manufacturer.

Checking your vehicle’s manual can help determine which type is best suited. Mixing 75w90 and 75w140 may often be a question, and the ultimate answer varies depending on the type of vehicle and driving conditions. Keep in mind the appropriate gear oil type for your vehicle to ensure optimal performance and longevity of your transmission.

How To Change Your Gear Oil

Changing your gear oil is an essential part of vehicle maintenance. To begin, gather the required tools and materials for the job. Safety is critical, so it’s important to take precautions such as wearing gloves and eye protection. Follow this step-by-step guide to successfully change your gear oil.

Keep in mind that mixing different gear oil weights can cause issues, so refer to the manufacturer’s recommendations and the ultimate guide before adding any oil to your vehicle. By following these guidelines and taking care during the process, you’ll be able to maintain your vehicle’s performance and extend its lifespan.

Frequently Asked Questions Of Can You Mix 75W90 And 75W140

Can I Mix 75W90 And 75W140 Gear Oils?

Yes, you can mix 75w90 and 75w140 gear oils. Mixing gear oils with the same api classification and viscosity ratings doesn’t usually cause any issues. However, it’s always recommended to consult your owner’s manual or a certified mechanic before mixing any gear oils as there might be specific requirements depending on your vehicle.

What Will Happen If I Mix 75W90 And 75W140 Gear Oils?

Mixing 75w90 and 75w140 gear oils doesn’t usually cause any issues as both have the same api classification and viscosity ratings. However, it’s worth noting that the mix can change the viscosity of the resulting fluid, which could potentially affect your vehicle’s performance.

It’s always recommended to consult your owner’s manual or a certified mechanic before mixing any gear oils.

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Is It Okay To Use A Heavy Duty Gear Oil?

Yes, using a heavy-duty gear oil like 75w140 is okay for most vehicles. Heavy duty gear oils are designed for high performance, high torque, and extreme temperature applications. However, it’s always recommended to consult your owner’s manual or a certified mechanic before switching to a heavier gear oil as there might be specific requirements depending on your vehicle.

Can You Mix Synthetic And Conventional Gear Oils?

Yes, you can mix synthetic and conventional gear oils. However, it’s important to note that mixing the two types of oils can affect the performance of the resulting fluid. It’s generally recommended to use the same type of gear oil throughout the vehicle, either synthetic or conventional.

Consult your owner’s manual or a certified mechanic if you’re unsure.

What Is The Recommended Viscosity For Gears?

The recommended viscosity for gears depends on the make and model of your vehicle. Check your owner’s manual or consult a certified mechanic for information specific to your vehicle. In general, 75w90 and 75w140 are common viscosities for gear oils.

Lower numbers indicate better performance in colder temperatures, while higher numbers indicate better performance in higher temperatures.


Mixing 75w90 and 75w140 is not recommended without consulting a professional mechanic. While both are high-performance gear oil types, they have different properties and are meant for different conditions. Mixing them could result in reduced performance or even damage to your vehicle’s transmission.

However, there are some instances where mixing may be acceptable, such as topping off an already mixed fluid. In such cases, it is important to ensure that the mixed fluid meets the specifications outlined in your vehicle’s manual. It is better to err on the side of caution and follow manufacturer recommendations to ensure the optimal performance of your vehicle.

Remember, investing in the right transmission fluid and maintaining it regularly will ensure the longevity of your automobile and save you money on costly repairs down the line. So, be wise and take proper measures while making such decisions.

Dustin Babich

Dustin Babich

Dustin Babich

As the passionate author behind, Dustin Babich is a knowledgeable expert in all things automotive. With a deep understanding of car tools, equipment, engines, and troubleshooting techniques, Dustin Babich shares invaluable insights, practical tips, and effective solutions to empower readers in overcoming car-related challenges.


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