7W90 vs 75W140: Which Gear Oil is Right for You?

Written by

Charles Bolte


Vernon Hoppe 

75w90 vs 75w140

When it comes to maintaining your vehicle, selecting the right gear oil for your automobile is crucial. Two popular options valued by most vehicle owners are 75w90 vs 75w140 gear oils. While the 75w90 is ideal for light cars, the latter is used for heavy-duty trucks.

Read more about oil number meaning and gear oil weight and highlight many more. Whether you own a Mustang, Jeep, or any vehicle requiring differential fluid, this will help you make a knowledgeable decision.

        Criteria 75W90 75W140
Viscosity at high temp Thinner viscosity Thicker viscosity
Extreme Pressure   Performance Moderate to heavy-duty applications For heavy-duty and high-torque applications
Temperature Cold temperature High-temperature environments
Fuel Efficiency Better fuel efficiency Slightly less efficiency
Cost Less expensive More expensive
Weight Chart Thinner viscosity, light-use vehicles Thickest type of 75, Heavy use vehicles
Fluid Change Interval Requires frequent changes Offers longer fluid change intervals

Basic Overview of 75W-140 Gear oil Vs 75w-90:


1. 75W-140 Gear Oil

75W140 gear oil is a high-performance lubricant developed for heavy-duty applications with extreme operating conditions. It is a thicker gear oil than 75W90, providing enhanced protection and stability under high-stress scenarios.

2. 75W-90 Gear Oil

75W90 gear oil is a versatile lubricant suitable for many applications, including passenger cars, light-duty trucks, and regular driving. Unlike 75W-90, it’s thinner gear oil and is not for heavily-used engines.

Performance and Oil Pressure


  • Gear oil viscosity is symbolized by two numbers separated by “W” (winter).
  • The first digit means the oil’s viscosity in freezing temperatures, while the second digit exhibits viscosity at operating temperatures.

75W90 and 75W140 are multigrade gear oils suitable for various temperatures. Their viscosity is the same when at low temperatures, as indicated in “75W”.

75W90 and 75W140 gear oils provide excellent lubrication and protect the drivetrain’s gears, bearings, and other components.

These gear oils use synthetic base oils or a combination of synthetic and mineral base oils, offering enhanced lubrication properties, more suitable thermal stability, and improved resistance to oxidation.

However, their performance characteristics differ due to their varying viscosities.

Differences Between 75W140 vs 75W90

1. Viscosity


The main difference between 75W90 and 75W140 is their viscosity ratings. The number 90 symbolizes a thinner oil compared to 140, indicating the oil’s resistance to flow.

So, between gear oil 90 vs 140, the higher the number, the thicker the oil, and gear oils with a “75” viscosity rating, 75W140, is the thickest gear oil.

2. Extreme pressure performance


75W1-140 gear oils have the highest viscosity for a “75” rating and are designed to handle heavy-duty vehicles due to their more aggressive performances, such as carrying hefty loads where the vehicle is experiencing extreme pressure.

75W-90 gear oils have lower viscosity, meaning the oil is thinner and can flow faster. 75W-90 gear oils tend to handle milder or tamer-used cars and are common in numerous vehicles.

3. Temperature


75W1-140 gear oils are more suitable for high temperatures because of the thickness of the oil made for heavily used engines.

75W-90 gear oils have lower viscosity, and the oil can flow faster and remain fluid at lower temperatures. It is excellent for cold weather.

4. Fuel efficiency


The higher viscosity of 75W-140 Oil can impact the fuel’s efficiency because of the oil’s thickness. The thicker the oil, the more internal friction will occur in the gear system.

75W-90 gear oils have lower viscosity and less thickness, reducing friction in transmitting power which is better for fuel efficiency.

5. Cost

Cost -of-75w140-vs-75w90-gear-oil

The cost of 75W90 and 75W140 gear oils varies depending on the brand, quality, and quantity. Generally, 75W140 gear oil tends to be slightly more expensive than 75W90 by about $10 – $15 per gallon, due to its higher viscosity and advanced formulation.

6. Fluid change interval

The 75W-90 gear oil frequently needs to be changed due to the oil’s low viscosity, which can thin the oil’s film quicker. 75W-140 delivers better pressure protection and is more durable, meaning you don’t have to change it too frequently.

7. Pros and Cons:

75W90 gear oil:

  • Improved fuel efficiency
  • Smoother gear shifts
  • Reduced power loss
  • Suitable for daily driving and commuting
  • Hardly provides optimal protection under extreme conditions or heavy loads.

75W140 gear oil:

  • Increased load-carrying capacity
  • Enhanced protection under high-stress conditions
  • Stable oil pressure in extreme temperatures
  • Suitable for heavy loads, towing, off-roading, and high-performance applications
  • Slightly reduced fuel efficiency
  • Thicker viscosity may result in increased drag

Application Suitability, Which is Right for You?


Choosing between 75W90 and 75W140 gear oils depends on your specific vehicle and its conditions. Here are some factors to consider:

1. Trucks and SUVs:


Trucks and SUVs are often used for towing, hauling heavy loads, and off-roading. Serious activities can pressure the drivetrain, requiring gear oils with high load-carrying capacity and exceptional protection.

75W140 gear oil is generally recommended for trucks and SUVs in these scenarios, as it offers superior resistance to extreme pressure and heat.

2. Performance cars:


High-performance vehicles, such as sports cars and luxury cars with powerful engines, can benefit from the added protection from the 75W140 gear oil.

The higher viscosity and enhanced film strength help withstand the stress from aggressive driving and more horsepower.

3. Recreational vehicles (RVs)


RVs often have heavy drivetrains due to their size and weight. Whether you have a motorhome or a towable RV, 75W140 gear oil ensures reliable lubrication and protection for the differential and other components, especially when towing or driving in mountainous terrain.

4. Off-road vehicles:


Vehicles dedicated to off-road adventures, such as dune buggies, and ATVs, encounter harsh conditions, uneven terrains, and extreme temperatures.

75W140 gear oil is well-suited for these demanding environments, as it provides exceptional protection and lubrication under intense stress and high temperatures.

5. Muscle cars:


Classic muscle cars, known for their powerful engines and high-performance capabilities, can benefit from the added protection and stability of the 75W140 gear oil. The thicker viscosity helps handle the increased torque and stress.

Frequently Asked Questions

What engine oil for a Mustang?

For most Mustang models, including daily drivers and those operated for spirited driving, 75W90 gear oil is often sufficient.

However, if you have a high-performance or track-focused Mustang, especially one equipped with a limited-slip differential, 75W140 gear oil might be a better option to withstand the increased stress and heat generated during aggressive driving.

What engine oil for a Mustang?

Jeeps, especially those used for off-roading or equipped with larger tires, require gear oils with high load-carrying capacity and resistance to heat. 75W140 gear oil is often recommended for Jeeps, as it provides better protection under extreme conditions and when towing heavy loads.

Can I use 75W90 gear oil instead of 75W140 in my vehicle?

Yes, you can use 75w140 instead of 75w90 and vice versa if you have no issue regarding viscosity.

However, using gear oil of lower viscosity than recommended can cause several problems. The lower viscosity reduces the lubricant’s ability to effectively protect moving parts from wear and tear, leading to accelerated wear on metal components and increased friction and heat buildup.

And if you used higher viscosity than recommended then it’ll be too thick to flow quickly enough to fill the spaces between the crank journals and main bearings while the engine is running. The engine will waste energy pumping the thicker oil, reducing fuel economy.

How often should I change the gear oil? 

The recommended interval for changing gear oil can vary depending on the vehicle make model, and usage conditions. For every 30,000 to 50,000 miles or every 2 to 3 years, manufacturers advised changing gear oils.

However, it’s crucial to consult the specific recommendations outlined in your vehicle’s owner’s manual or contact the manufacturer for accurate information.

Can I mix 75w-90 and 75w-140? 

Mixing different viscosities of gear oils can lead to unpredictable results and potentially compromise performance and is not recommended to do. However, in some cases, a limited amount of mixing between 75W90 and 75W140 gear oils may be acceptable.

It is advisable to consult the manufacturer’s recommendations or seek professional advice before combining gear oils.

How do I check the gear oil level? 

Locate the fill plug or dipstick, clean it, reinsert it, and check the oil level. Add if necessary to reach the recommended range.


Choosing between 75W-90 vs 75W-140 gear oils depends on your vehicle’s requirements and usage. If you prioritize fuel efficiency, smoother shifts, and everyday driving, 75W-90 is more suitable.

For heavy loads, towing, off-roading, or high-performance applications, 75W-140 provides increased protection and stability under extreme conditions. It is essential to refer to your vehicle manufacturer’s recommendations and consult professionals to know the right gear oil for your exact vehicle and driving needs.

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