75w140 Vs. 75w90 – An In-depth Comparison

Gear oil is essential for manual transmission units, differentials, and transfer cases of your car. Like engine oil, gear lube is handy for wear protection, heat dissipation, and expulsion of contaminants. You need to pick the right gear oil for your vehicle depending on your driving conditions, which brings us to the 75w140 vs. 75w90 discussion.

As a regular motorist, there is a high chance you have encountered 75w140 and 75w90 gear lubricants. So, which is the befitting oil between the two? An extensive review of 75w140 and 75w90 will provide the necessary info to guide you on the best pick.

What Is 75w140?

75w140 is a dense and heavy-duty application gear lubricant. The numbers and letters hint at the lubricant’s performance in different conditions. 75 is the oil’s viscosity index in low temperatures, the W stands for winter, while 140 is its viscosity in high temperatures.

75w140 has a decent temperature operating range, courtesy of its viscosity. It is ideal for low temperatures, as it remains stable up to -40⁰ Fahrenheit. Unlike other lubricants with lower density, 75w140 won’t freeze in cold conditions, an edge of efficiency. 

On the hotter side, 75w140 is stable up to 405⁰ Fahrenheit, depending on its formulation. It will flow effortlessly and still be thick enough to dissipate heat and prevent friction. Please note that the temperature range may vary slightly depending on the manufacturer’s formulation.

What is 75w140 used for? This lubricant is highly adaptable, supported by its thickness, and you can use it for extreme driving temperatures, hot and cold. Its vast operating temperature range makes it perfect for heavy-load manual transmission applications.

Common Brands Of 75w140 Gear Oil

You should always go for top-rated gear oil brands that guarantee the best service. Several oil brands stock 75w140 gear oil: you pick the best brand depending on price, quality, availability, and formulation.

Valvoline is a notable oil manufacturer that does not compromise on quality. The Valvoline full synthetic 75w140 lubricant is top-grade, with a sulfur-phosphorus and synthetic base oil formulation. The sulfur and phosphorus compounds enhance the oil’s anti-wear properties and increase its loading capacity. Furthermore, this Valvoline product assures you of extreme pressure protection and anti-foam performance.

The Mobil 1 Syn gear lube LS 75w140 suits modern high-performance passenger cars. It will extend gear, seal, and bearing life, courtesy of its excellent thermal stability and high-temperature oxidation resistance. This gear oil is highly resistant to foaming, ensuring all-around lubrication. This Mobil 1 lube will regulate rusting and has tremendous limited slip performance.

Still, under Mobil, you have the Delvac synthetic 75w140 gear oil built for heavy-duty commercial vehicles. The lubricant’s viscosity shield is the vehicle’s drivetrain against severe pressure and shock loading.

Royal Purple’s Max gear 75w140 high synthetic gear oil is fit for truck and cars’ manual transmissions and front or rear differentials. This product will maximize your vehicle’s horsepower, reduce operating temperature, and control corrosion. A friction modifier in the oil increases its lubricity to contain wear and tear.

Other 75w140 brands include Castrol, Motorcraft, and Lucas Oil. Always go for manufacturer-recommended products for efficiency.

Equivalent Oil

Depending on your driving conditions, you may substitute 75w150 gear lube with other equivalent options. 75w90 is ideal for driving in cold conditions, as they have the same low-temperature viscosity index. For hotter environments, you can go for 80w140, which has the same high-temperature index as 75w140. Moreover, it does an excellent job in light to heavy vehicles.

75w140 vs. 85w140, are they compatible? 85w140 has a cold temperature index of -10⁰ to 0⁰ Fahrenheit, and a high temperature viscosity index of 405⁰ Fahrenheit. You can use 85w140 instead of 75w140 in hot conditions, but it won’t perform as well in cold weather.

Seek professional advice if you are unsure about the substitute to avoid mishaps with your vehicle’s transmission unit.

Pros Of 75w140 Gear Oil

75w140 is highly versatile, evident from its massive operating temperature range of -40⁰ to 405⁰ Fahrenheit. It is stable when it is cold or hot. This lube performs exceptionally well in hot temperatures due to its thickness. It flows smoothly, protecting the moving parts from friction, heat buildup, and oxidation.

75w140 is compatible with various types of cars, from passenger cars and light trucks to vans, buses, and heavy commercial vehicles. This lubricant is resistant to thermal breakdown, a reason why it is the go-to option for heavy-duty applications or use in hot weather.

Cons

As hinted earlier, 75w140 is viscous, which works for it in some situations but fails in some, such as in icy conditions. While it remains stable for temperatures as low as -40⁰ Fahrenheit, it may present some hiccups. 

This lubricant is quite pricy as it has numerous applications. Additionally, it does not fare well in fuel economy.

What Is 75w90

75w90 gear oil is a fully synthetic multigrade lubricant suitable for cold environments, supported by its low viscosity. Its thickness allows it to remain stable when temperatures fall without freezing. Breaking down 75w90, 75 is its low-temperature viscosity index, W stands for winter, and 90 is its high or operating temperature rating. Its operating temperature range is -40⁰ to 302⁰ Fahrenheit. 

This lube has multiple uses, primarily in manual transmission units of passenger vehicles. Other areas of application include transfer boxes of four-wheel and all-wheel drive powertrains and front and rear automotive differentials.

Despite having a vast operating temperature range, it works better in cold and warm environments. Its formulation is a significant contributing factor to its stability in freezing conditions.

75w90 vs. 80w90, what is the difference? These two gear lubricants share similarities, like their suitability for cold and warm weather. The main difference is their low-temperature stability. 75w90 flows freely up to -40⁰ Fahrenheit, while 80w90 is good for -20⁰ Fahrenheit and higher. They have similar operating temperature values.

Common Brands Of 75w90 Gear Oil

It is advisable to stick to the 75w90 gear oil brand recommended by your car’s manufacturer. Several oil companies stock 75w90, with Amsoil being one of the prominent names to rely on for gear lube. Its SEVERE GEAR 75w90 is perfect for high-load demands.

This Amsoil product performs excellently in extreme temperatures, with its thermal stability being handy against acidity and carbon buildup. Its additives coat the gear surfaces with an iron-sulfide barrier, cushioning them from pitting and scoring.

ExxonMobil enters the discussion with the Mobil 1 Syn Gear lube LS 75w90 for superior performance in modern passenger cars. This Mobil 1 gear lubricant contains sulfur-phosphorous additives for comprehensive support of differentials and rear axles. Its formulation boosts its effectiveness in heat dissipation and averting oxidative deterioration.

Royal Purple’s Max Gear, 75w90 gear oil, ticks the boxes of versatility, safety, and efficiency. Versatility is evident from its functionality in hot and cold conditions and suitability for light and heavy-duty automobiles. In addition, this lubricant won’t damage parts made of soft yellow metals like brass and copper.

Royal Purple relies on its proprietary Synerlec technology, focusing on additives that enhance its lubricant’s effectiveness at the molecular level. The oil creates strong ionic bonds with the metal surfaces, boosting their resilience against heat and pressure.

You may also check out Valvoline SynPower 75w90 full synthetic gear oil, Lucas 75w90 synthetic oil, and Red Line’s GL-5 gear lube.

Equivalent Oil

Several gear oil grades match the performance of 75w90, making them suitable substitutes. Your replacement choice depends on viscosity levels in varying conditions. For winter driving, your options include 75w80, 75w85, and 75w140, as they all have similar low-temperature viscosity indexes.

75w140 might be too thick, but it is more adaptable, with a vast operating temperature range, and works fine in hot weather. 85w90 and 80w90 are great alternatives, particularly for cold to warm conditions, but they won’t perform as well when it is freezing.

Pros Of 75w90 Gear Oil

75w90’s low viscosity is its primary appealing element. This lubricant will flow in chilling conditions of up to -40⁰ Fahrenheit, with its thinness contributing to an excellent fuel economy.

75w90 works well in hot temperatures, up to 302⁰ Fahrenheit, courtesy of its thermal stability. It withstands heat and pressure without forming deposits or breaking down. Additives in this gear oil enhance its functionality, especially in wear protection. 

This gear lube is versatile with vast applications from vehicle manual transmission units, differentials, and transfer cases to heavy-duty industrial gearboxes. 

Cons

75w90’s viscosity is also its undoing, especially when it is hot. While it offers adequate protection when temperatures rise, it is not at the same level in chilly conditions. 75w90 comes short in heavy-duty applications.

75w140 Vs. 75w90 Differences

Understanding the 75w140 vs. 75w90 differences will help you determine the befitting gear lube for your car. Similarities between the two oils include their cold viscosity index and diverse operating conditions, among many more.

The differences dictate their respective applications.

Specifications

Viscosity

Viscosity focuses on how fast oil flows at various temperatures and is a huge determinant of its applications. 75w140 and 75w90 have similar low-temperature resistance and will flow at extremes of -40⁰ Fahrenheit though the former is more viscous in standard and high temperatures.

Kinematic viscosity is crucial when comparing the two lubricant grades and looking at their resistance under the influence of gravity. 75w140 has a higher kinematic viscosity, making it thicker with increasing temperatures.

The thickness of 75w140 makes it the best pick for high-temperature applications, as it will do an excellent job of wear protection and heat dissipation. Additionally, it is great for heavy-duty settings, like in larger vehicles or off-roading.

On the other hand, 75w90 works well in colder environments due to its thin profile. It is advantageous as it is less prone to gelation when freezing. 75w90 remains thin even when temperatures rise, lowering its protective capabilities.

Density

75w140’s density is roughly 0.9 g/cm3 at 59⁰ Fahrenheit, which is more than 75w90’s, at around 0.87 at the same temperature. Density directly affects viscosity: denser liquids are more viscous. While the density margin between 75w140 and 75w90 is not that much, it is significant and affects their performance under diverse conditions. 

Density affects the oils’ functionality in many ways. First, a dense lubricant circulates slowly, which can affect a vehicle’s performance in the cold, as it may gel. Less dense lubes will flow smoothly and stay stable when temperatures drop.

Moreover, density determines the lubricant’s interaction with parts, such as the gears, gaskets, and seals. High-density oils provide thick films that offer maximum protection and seals. The thickness can be problematic when it causes the oil to push excessively against seals leading to leaks.

Additives

75w140 and 75w90 contain various additives that perform several functions. They may boost the desirable properties of the base oils, eliminate their bad characteristics or add new functionality facets. The most common gear oil additives include:

The type and concentration of additives depend on the gear oil brand and purpose. Typically, 75w140 contains more additives than 75w90 to sustain its heavy-load uses. 

Operating Temperature

Adaptability is a key selling point of the two gear oils, evident from their wide operating temperature range. They are multigrade lubricants suitable for cold and warm driving environments. 

75w140 and 75w90 have the same cold temperature viscosity index, as denoted by the first number before the letter, and circulate freely up to -40⁰ Fahrenheit. The difference is in their hot temperature index. 75w140 has a higher index of up to 405⁰ Fahrenheit, whereas 75w90’s is at 302⁰. 

75w140 adapts well to rising heat by getting thicker, which is necessary for maximum wear control. 75w90’s is thin, even when it gets hotter; thus, it comes short of 75w140’s performance, though it does well in the cold.

Price

A keen product comparison reveals that 75w140 is pricier than 75w90. 75w140 costs more due to its formulation and additives used. As earlier hinted, it has more additives for efficiency. 75w140’s diverse applications are another reason why it is costlier than its counterpart. The prices vary depending on the brand.

Don’t pick 75w90 because it’s cheaper. Always go for the recommended oil for your gears’ best shape.

Which One Is Suitable for You?

75w90 vs. 75w140, which one should I go for? You must consider several factors to determine the befitting gear lubricant. Start by factoring in your area’s climate. Cold conditions affect oil performance, as they may cause gelling, the solidification of oil. Gelled oil won’t adequately circulate, and driving may be challenging.

75w90 and 75w140 are suitable for chilly conditions and can withstand extremes of around -40⁰ Fahrenheit. 75w90 maintains its low viscosity, more than 75w140, making it the best pick for the cold. 75w140’s is the go-to alternative for hot weather, as its density increases with heat, resulting in excellent wear defense. 

You should also consider the area of use. The less-dense 75w90 is ideal for light vehicles and motorcycles. 75w140 works well in heavy-duty, off-road, and high-performance automobiles. 

Stick to your vehicle’s manufacturer’s gear oil suggestion. If unsure, seek advice from a qualified professional.

FAQs

What Gear Oil Should I Use in My Differential?

Lubrication is a critical maintenance routine for your vehicle’s differential. You use gear or differential oil for this practice, as indicated by your car’s manufacturer. You can refer to the vehicle’s manual to know the befitting oil grade.

Factors determining the lubricant to go for include the type of differential, running conditions, and climate. 75w90 gear lubricant is the best option if you have a non-limited slip differential. For limited slip differentials, you use 75w140 due to its anti-friction additives that ensure smooth operation.

On running conditions, 75w90 works fine for daily driving and light duties. You will require 75w140 for heavy-duty tasks, off-road driving, and racing. For cold climates, 75w90 is the best selection for your differential, as it is less dense, whereas the heavier 75w140 is fit for hot environments.

What Is 75w140 Oil Used For?

75w140 is multi-grade gear oil with plenty of uses, a reason many motorists prefer it. It works fine in cold and hot environments, a -40⁰ to 405⁰ Fahrenheit, a wide operation range. 75w140 becomes thicker with increasing temperature, amplifying its protective qualities.

This lubricant is perfect for high-resistance driving conditions, such as racing, off-roading, and towing or carrying heavy loads, courtesy of its thermal resiliency and stability.

Can You Mix 90 And 140 Gear Oil?

Mixing gear oils of different grades is not advisable as you may affect their respective performance. 90 and 140-grade gear oil have varying heat resistance levels and formulations, especially if they are from different brands. The resulting mixture may be lighter or heavier than needed or with a compromised additive formulation. This situation may lead to the degradation of associated components.

Is 80w90 Thicker Than 75w140?

80w90 has a low viscosity; as such, it works well in cold climates due to its low freezing point of around -18⁰ Fahrenheit. It can also withstand higher temperatures, a maximum of 302⁰ Fahrenheit, though its lightness hinders its functionality in such conditions.

75w140 is thicker and more flexible than 80w90, remaining stable between -40⁰ and 405⁰ Fahrenheit. It becomes more viscous with heat increase; hence, suitable for demanding tasks.

Is Heavier Gear Oil Better?

Whether or not to use heavy gear oil relies on environmental and driving conditions. Viscous gear oil is better in high temperatures, with its thickness aiding heat transfer and shielding the moving parts from tear. Moreover, it is an excellent alternative for large commercial vehicles like trucks, racecars, and rough road driving, with viscosity being crucial for shock absorption.

Avoid using dense gear oil in the cold, as it is likely to solidify and fail to circulate. When buying gear oil, you should check their viscosity grades to get the correct item.

Is Higher Number Gear Oil Thicker?

Gear oils have grades that indicate their viscosity index. Typically, the first number indicates the oil’s index when it’s chilly, and the last figure is its operating or warm temperature index. 

The higher the first number, the less viscous the lubricant is and the more suitable it is for cold environments. Oil grades with a higher last number are thicker and built for the heat and demanding conditions. 

What Happens If You Use the Wrong Gearbox Oil?

Using the wrong gearbox lubricant can adversely affect your vehicle’s performance. Poor lubrication is a common problem you will encounter from this mistake, noticeable through noise production and difficulty changing gears.

Leaking is another possible outcome of using incorrect lube, primarily if it is less dense than the recommended one. The wrong product may fail to provide adequate lubrication, leading to heat buildup, which can damage components like gears and seals.

You should flush the gearbox to eliminate the wrong oil immediately after you notice the mistake and use the proper lubricant. In case of any issue after the flush, you should consult a professional for help.

Final Words

Weather, driving condition, and car type are crucial determinants for the correct gear lubricant, primarily focusing on the effect of viscosity. The 75w140 vs. 75w90 comparison shows their differences and areas of use. Key takeaways include their similar low viscosity index, wide operating heat range, and 75w140’s superiority in heavy-duty settings.

Can I use 75w140 and 75w90 interchangeably? You can swap them if driving in icy weather, as both have the same low-temperature stability value. However, you should stick to 75w140 if moving in hot environments or handling challenging tasks, as it can keep up with the demands.

You should consult your mechanic or vehicle dealership for a suitable gear lubricant to avert costly mistakes.