75w90 vs. 80w90: A Comparison of the Gear Oils

Lubricants and gear oil play a crucial role in car components. It protects the gear components from rust, corrosion, and oxidation, thus enabling them to run smoothly. You find these gear oils in different weights. The applications of these oils differ based on their viscosity. This brings us to the comparison of 75w90 vs. 80w90 gear oils to find which one is preferable for our specific needs.

The transmission units work at high temperatures, pressures, and speeds, thus the need to use the proper transmission oil. Some people use 75w90 and 80w90 interchangeably but are this right? While these oils are made with similar components and performance booster additives, their viscosities are different, thus affecting their functionality under different temperatures.

High viscous gear oils provide better performance due to their consistency. However, this may affect the gear’s efficiency due to thickening during cold and moderate temperatures. Therefore, how do you decide which gear oil to use? Here is all we require to know about 80w90 and 75w90 gear oils.

Read Also: Can You Mix Different Brands Of Oil?

75w90 vs 80w90 gear oil

75w90 Gear Oil

What does 75w90 mean? 75w90 gear oil is a synthetic gear lubricant made entirely from synthetic base oils and additives. We use the gear oil in applications with extreme pressure. It is recommendable for use in colder climates and limited-slip differentials. 75w90 is ideal for axles, final drives, and heavy-duty manual transmissions.

The 75w90 gear oil is a multipurpose, high-performance one that features an anti-friction treatment. This gear oil is designed for use on lots of railway gearboxes. It presents incredible load spotting functionality where surprise loading and severe pressures are expected.

75W90 oil features excessive viscosity index (VI), oxidation, thermal stability, and extraordinary low-temperature fluidity, and low pour point. The significant benefit of the 75W90 gear oil is its excellence in foaming, offering long seal life and excellent film strength maintenance, thus enhancing reliable lubrication.

80w90 Gear Oil

80w90 synthetic oil can be used both as a lubricant for non-synchronized manual transmissions for busses and trucks and in extreme-pressure applications. The 80w90 is recommendable for limited slip and conventional differentials. The 80W90 has two viscosity grades. The W shows how the oil is stable during the winter season.

The 80 shows that the oil works excellently in cold temperatures, while the number 90 denotes the 80w90 gear oil viscosity or thickness at 100% degrees Celsius. Therefore, the kinematic viscosity of 80w90 gear oil ranges between 13.5 to 18.4 square millimeters/second. This oil features high shear stability and withstands heavy loads.

Thinner oils work more freely and smoothly in low temperatures. This makes 80w90 synthetic gear oil multipurpose since you can use it on gears, axles of spirals, and some manual transmissions. This gear oil has exceptional flexibility and strong resistance to foams and defends parts against corrosion.

Read Also: Synthetic Oil vs. Conventional Oil

75w90 vs. 80w90 Differences

Gear oils may look similar since they are all in liquid forms, but they differ significantly. The use of gear oil is determined by its grade or SAE number. 80w90 and 75w90 gear oil vary considerably in their usage, configuration, ingredients used, and other things you cannot see. Let us see in detail what brings the difference between 75w90 vs. 80w90.

can i use 80w90 instead of 75w90

1. Viscosity

One notable difference between 75w90 and 80w90 gear oils is their thickness, also known as viscosity. Gear oils have been historically known for fleet operators and proprietors since they have better viscosity. Gear oils are made to maintain axle machinery even in highly challenging situations.

The SAE 80w90 is made from mineral oils. This gear oil is denser compared to 75w90 at lower temperatures. This means that it requires more frequent oil adjustments and, thus, more maintenance. It’s thickening at lower temperatures may degrade its efficiency level, thus affecting its production.

On the other hand, 75w90 denotes a constant viscosity, thanks to its wide range of temperature preservation. Therefore, this gear oil is more efficient than the 80w90 gear oil in both hot and cold seasons.

2. Density

The thickness and density of gear oils are related to each other. It means that gear oils with more density are certainly thicker. The 80w90 gear oil provides a density of 0.90, while the 75w90 gear oil provides a density of approximately 0.86. Thicker gear oils are more advantageous since they offer better protection than thinner oils.

However, thicker oils get clumpy at lower temperatures, thus downgrading efficiency. Though the 75w90 gear oil is thinner, it offers adequate protection in extreme weather conditions and maintains your vehicle parts’ efficiency.

3. Additives

Both 75w90 and 80w90 perform almost equally in terms of efficiency and composition. 75w90 gear oil features a particular adhesive packaging that coats gears and inhibits them from wearing out. This gear oil is exceptionally reliable, non-foaming, and sleek, thus ideal for heavy-duty applications. It offers high efficiency and is made to withstand extreme temperatures while still lubricating.

80w90 is strengthened with lubricating and anti-wear agents, which helps manage gear wear and tear. This gear oil also features heat control additives which are difficult to get in other basic gear oils. 80w90 gear oil is ideal for racing vehicles and other heavy-duty use where other oils fail to perform sufficiently.

4. Operating Temperature

75w90 is thermally robust, thermally stable, stable shear, and para-synthetic. This gear oil is multi-grade, and it is ideal to use in all types of vehicle drive applications. The best gear oil should be able to work even under extensive ambient temperature ranges. It can stand as high temperatures of around 300F to 350F.

80w90 synthetic gear oil is more versatile and thus operates in both extreme environments. This gear oil works perfectly on temperatures ranging from -20F to 400F. This means that it is the most recommended gear oil in summer and winter weather conditions. 80w90 gear oil features a higher rating compared to 75w90.

5. Uses

Since 75w90 and 80w90 gear oils differ in density and viscosity, they behave differently when placed in extreme conditions. This brings out the differences in their use. 80w90 is the most preferred gear oil to use during summer and winter.

This is because it is made to withstand both extreme weather conditions. You can use 80w90 gear oil for manual gearboxes, agricultural equipment, transaxles, and transfer cases in passenger vehicles, trucks, 4WDs, and light commercials.

75w90 covers a wide range of temperatures but is ideal for higher temperatures. The gear oil minimizes premature wear and tear in your gear system in high temperatures. This gear oil is recommended in heavy-duty manual transmissions, axles, and final drives.

6. Price

We cannot look at the comparison between 75w90 vs. 80w90 gear oils without talking about the price. We all want to buy a product that will cut our overall cost and the maintenance cost. 75w90 has constant viscosity and thickness in a broad spectrum of temperatures.

The oil becomes thinner at very low temperatures and thicker at extremely high temperatures. These dynamics are what make 75w90 gear oil a little expensive. It is a little pricier compared to the 80w90 gear oil cost. Though 75w90 is costlier, it is worth it.

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Frequently Asked Questions (FAQs)

Q: Can you use 80w90 instead of 75w90?

You can use 80w90 instead of 75w90. However, it is good to consider the conditions under which you will be using them. 80w90 gear oil has a higher viscosity than 75w90. Therefore, if you will be experiencing either of the extreme weather condition, 80w90 is the way to go.

Q: Which is better, 75w90 or 80w90?

Which is better between 75w90 and 80w90 will depend on what you want to use as the gear oil. In many instances, the 75w90 beats 80w90 gear oil which is more stable in different temperatures. It is, therefore, most ideal for preventing wear and tear in high temperatures.

80w90 is denser and works well in both high and low temperatures. It, however, requires high maintenance since it is mineral oil. Most experts believe that 75w90 gear oil is more efficient and gives you value for your cash.  

Q: Can you mix 75w90 and 80w90?

You can mix 75w90 and 80w90 gear oils since they do not differ too much in additives. Mixing the two may not downgrade your vehicle’s performance. However, it is advisable to consult your vehicle manufacturer’s manual or mechanic before mixing the two gear oils.

Q: Is it bad to mix gear oil?

Mixing gear oils will depend on the types of oil you want to mix. You can mix esters, PAOs, and mineral oils. However, you should not mix PAG (polyglycol synthetic oils).

Mixing the wrong types of incompatible oils makes them react, thus forming some gum gels on the vehicle parts. It is, therefore, recommendable to consult with your mechanic before mixing any gear oils.

Q: What’s the difference between gear oil and hypoid gear oil?

Hypoid gear oil is an oil for the gearbox, but the ingredients are different from regular gear oil. These gear oils are made to function with the hypoid gear designs effectively.

The gear oil is mixed with additives meant to increase its breakdown resistance for the sliding surfaces in the gear mesh. The Extreme Pressure (EP) additive enables it to work effectively under high mechanical pressure and temperatures produced in hypoid gearboxes.

Q: What is the difference between gear oil and differential oil?

Differential oil can sometimes be referred to as gear oil. Differential oil is found in the axle housing. This oil is made to work under high-pressure circumstances instead of in high-temperature situations. The oil is poured on the rear differential housing, lubricates the gear bearing, and clutches in the rear end.

Final Words

80w90 and 75w90 are both synthetic oils made of identical components, and the same additives were added. The oils, however, are used in different applications depending on their capabilities. The 75w90 vs. 80w90 comparison shows us the difference between the gear oils. The latter is denser and provides better protection in extreme weather conditions 75w90 gear oil is thinner but more stable. It is the most preferred gear oil for adequate protection, especially in high temperatures. You will, however, require to add a little more coins to buy the 75w90 gear oil.

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Purity Wachira

Hi, I am Purity a researcher and technical writer since 2015. I hold a Masters in Supply Chain Management working in an automotive company. I am a resourceful lady with vast knowledge and interest in vehicles. My enthusiasm for cars drove me to more research, and the more information I got, the more I felt the need to share the knowledge through writing. My biggest win is to leave a positive impact on the automotive field and solve people's problems through articles, product descriptions, and product reviews.

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