Gear oil protects your vehicle’s transmission, drive axles, and gear from malfunctioning during daily use. In different situations, your car needs different gear oil grades.
Many people need clarification about the difference between 75W-90 vs. 75W-140 gear oil. While most car owners know about this, that doesn’t mean learning their differences is not a good idea. If you acquire more knowledge about them, you can care for your car more.
In both cases, the first number is the viscosity rating, which determines how thick or thin it is. However, please keep reading if you want to know their key differences and more critical information.
Differences Between 75w90 Vs. 75w140 Gear Oil
If we look at 75w90 and 75w140, we discover that the main difference is the running temperature.
A 75w140 contains higher viscosity than a 75w90. It’s because 140 means it takes 1 second for 140 ml to flow through an opening. On the other hand, 90 means it only takes 90ml to flow through the same space. So, 90 of 140 provides different viscosity as we know.
You can expect the same density from them. 75w90 will have lower viscosity at higher oil temperatures than 75w140. However, both show the same thickness at lower oil temperatures. Let’s dig deeper to discover the suitable and most compatible gear oil for your vehicle.
| Grade | SAE 75W90 | SAE 75w140 |
| Density 15 C, g/cm3, ASTM D4052 | 0.86 | 0.89 |
| Flash Point, Cleveland Open Cup, °C, ASTM D92 | 210 | 203 |
| Kinematic Viscosity 100 C, %, ASTM D445 | 15.7 | 25 |
| Kinematic Viscosity 40 C, mm2/s, ASTM D445 | 115 | 182 |
| Pour Point, °C, ASTM D97 | -45 | -45 |
| Viscosity Index, ASTM D2270 | 144 | 170 |
What Is 75w90 Gear Oil?
75w90 is a fully synthetic gear lubricant made from synthetic crude oils and a highly refined extra skim. Also, it’s assembled to have an appreciable load-bearing capacity even under severe stress. It also has many uses in many railway gearboxes.
Additionally, this 75w90 synthetic gear oil provides superior heat resistance or heat stability and oxidation stability. This gear oil occurs as a chemical reaction when the lubricating oil is exposed to oxygen. Some of the excellent features of 75w90 are its high viscosity index. Actually, it’s also known as VI means shallow pour point and unstable at low temperatures.
Related: 75W90 Vs. 80W90 Gear Oil: Which Is Better?
What Is 75w140 Gear Oil?
75w140 is a fully synthetic drivetrain lubricant formulated to satisfy challenging operating standards.
This particular product is formulated for use in robust and heavy-drive trains. Likewise, it requires proper gear insulation with relatively high viscosity and exceptional load-carrying capacity and stability.
Also, this Synthetic Gear Oil 75W140 combines synthetic stock oils and well-developed additives and preservatives. Besides this, it provides some significant advantages that mineral gear oils lack.
Contemporary and up-to-date equipment gear Oil 75w140 performs well over a wide range of temperatures. Furthermore, it can resist any damage caused by corrosion or heat and maintain oxidation stability.
What Does The Number Mean In Gear Oils?
According to their viscosity, the Society of Automotive Engineers (SAE) has adopted a grading system for engine and gear oils.
Moreover, according to the viscosity grading principle, every fluid is classified into two categories: monograde and multigrade.
The Viscosity Of Gear Oils
Only those assigned with a number without the letter “W,” for example, SAE 80, SAE 90, SAE 140, etc., are specified at 212°F or 100°C. These gear oils perform well at high temperatures.
In contrast, the gear oil’s viscosity is designated with a number followed by the ” W” letter. For example, there are SAE 70W, SAE 75W, SAE 80W, etc., with a specific temperature of 0°F or 18°C. The letter “W” stands for winter, and they work well at low temperatures.
When to Use 75W-90 Oil
Generally, automotive gear oil is two types: One for the front axle, which is a 90 viscosity grade, and another one for the differential or rear axle and heavy load manual transmission, which needs a 140 viscosity grade.
75w90 is versatile gear oil and can be used in many applications. It’s also less likely to overwork your engine. If you are searching for a more versatile gear oil, 75w90 gear oil is a better choice.
Most importantly, you also can use this 75w90 gear oil in most environments, although it starts to struggle at high temperatures. Consequently, you can use this Oil in a temperate climate. You can also use it on gearboxes with API GL-5 performance limits.
When to Use 75W-140 Oil
SAE 75W-140 oil is commonly used as differential or rear axle oil for many passenger vehicles and trucks with very high horsepower. Also, these differential high-viscosity base stocks help to protect gears by maintaining a film of Oil. In addition, high-pressure agents are used to decrease metal-to-metal wear.
Generally, it is a strong option for highway manufacturing, agriculture, and construction. However, it would be best to remember that it can struggle at low temperatures.
Pros And Cons Of 75W-90 and 75W-140 Gear Oil
Here we have discussed the pros and cons of both gear oil.
| Name Of Oils | Pros | Cons |
| 75w90 Gear Oil | This gear oil offers more excellent fuel economy than other oils. Even so, it performs better than other oils when the temperature is low. | It thickens at high temperatures, and as a result, it struggles at elevated temperatures compared to other oils. You can expect these gear oils to lose their viscosity quickly when you put them under heavy loads. |
| 75w140 Gear Oil | Basically, this oil is thinner at higher temperatures. As a result, it can work excellently in hot weather. Optimal for longevity and wear. | The fuel economy is weak like others and works well at low temperatures. You may notice that 75w90 gear oil works well at cool temperatures, while 75w140 works well at high temperatures. |
The Comparison Between 75w90 Vs 75w140:
Viscosity
Gear oil is a special lubricating agent for transmission in cars such as trucks and various parts of machinery. Gearboxes lack an oil pump, so high viscosity is needed to deliver the oil.
High speeds require low-viscosity gear oil. Low viscosity causes less friction. Similarly, low density enhances the machine’s or vehicle’s mechanical efficiency and offers excellent cooling conditions. In contrast, high viscosity is helpful for low speed. High viscosity gives thick oil film high friction even at high pressure.
Both 75w90 and 75w140 contain the same viscosity at low oil temperatures. 75w140 has a more significant scale viscosity – meaning it performs better over a more comprehensive temperature range.
Fuel Economy
75w140 is a heavier viscosity used for more flexible and harsh services. Additionally, it’s only recommended for severe towing and constant use. 75w90 is recommended for regular service and infrequent towing.
Operating Temperature
The main difference between 75w90 and 75w140 is that at operating temperatures. 75w140 will be significantly thicker than 75w90. Nevertheless, at room temperature, they will both have the same density.
Pricing
In standard measurements, 12 bucks for a quart of 75w90 and 20 bucks for a quart of 75w140. In particular, 75w140 is a bit more expensive because they have different uses. On the contrary, you can use 75w140 for heavy towing and 75w90 for regular use.
Which Is Better, 75W-90 or 75W-140?
If you’re trying to find which is better, pay attention to them. Both types of gear oil have their weaknesses and strengths. Consequently, you should consider what your current situation is. Typically, if you live in a winter environment, you can use 75W-90 gear oil. But if you operate in a hot climate, you must use 75W-140.
Another thing to consider is whether you will perform heavy-duty work. If so, you should lean towards using 75W-140.
75w90 vs 80w90
In mineral gear oil, there is a big difference between a 75W90 and an 80W90. A mineral 75W90 may contain large amounts of polymer viscosity index improvers that will shear over time. Generally, the base oil mix is much lighter, so your gear oil will thin out significantly over time.
An 80W90 contains a higher viscosity base oil mix and will have a much lower polymer VII to shear. Hence, it will become more consistent in its viscosity over time.
Moreover, a thicker base oil mixture will afford better protection for the gears. Synthetic gear oil uses almost no polymer VII to get 75W90, and a high-quality synth will use no VII.
FAQ (Frequently Asked Questions):
Q. What is 75W140 used for?
SAE 75W-140 is commonly used for many passenger vehicles and trucks with high loads or very high horsepower. High-viscosity base stocks help protect gears by maintaining an oil film to reduce metal-to-metal wear.
Q. Is Thicker gear oil better?
High-viscosity gear oils provide thicker films, better wear resistance, and corrosion protection. And it makes them suitable for slower gearboxes operating under more severe stresses and loads. They seal components better and carry changeover intervals.
Q. Can I use 75w140 instead of 75w90?
Most people won’t notice much difference when switching between oil types. As a result, you will change from 75W-90 to 75W-140. Remember that you should be aware of the climate you live in.
Additionally, if you want to run a heavy-load engine, switching to 75W-140 makes sense.
Q. Can you mix 75W90 and 75W140?
Sticking with the same gear oil allows your car to be more efficient. That’s why you should be fine if you accidentally mix the two oil types.
The possible result is that the two oils will mix in your car. Mainly, this means it will have the same effect as 75W-115 gear oil. This number is directly in the middle.
If you mix oils with different viscosity ratings, you may run into problems. But that shouldn’t be a problem since they have the same rating.
Final Word
In summary, a 75w90 grade lubricant is ideal for daily passenger vehicles. Although 75w140 Oil is recommended for high-performance and heavy loads, pickup trucks produce higher horsepower.
Ultimately, your car’s mechanical components need help lubricating during cold starts. An oil with low viscosity, such as the 75w90 range, prevents mechanical wear. During Summer, You need a lubricant that can handle the extra heat without thinning or burning. And that’s where a 75w140-rated gear oil will be best.