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The Difference Between GL-4 and GL-5 Gear Oil

Written by Charleen

The Difference Between GL-4 and GL-5 Gear Oil

The main difference between GL-4 and GL-5 gear oils is in the level of extreme-pressure (EP) additives.

It’s really very simple. They are not interchangeable and GL5 didn’t replace GL4.

by Eddie Yorkman,|July 5, 2022

If you’ve ever purchased gear oil, or spent any time looking at gear-oil specifications, you have undoubtedly come across the API GL-4 and GL-5 specifications. You may have wondered, what is the difference between GL-4 and GL-5 gear oil? Where can I buy GL-4 and GL-5 gear oil?

Severity – Hypoid gears vs Helical

The American Petroleum Institute (API) classifies gears using GL ratings, ranging from GL-1 to GL-5. Higher GL rating numbers represent more severe applications; GL-1 is the least severe and can usually be satisfied with a motor oil, while GL-5 is the most severe GL rating.

EP additives

The main difference between GL-4 and GL-5 gear oils is in the level of extreme-pressure (EP) additives. EP additives effectively protect gears by providing a sacrificial layer on gear surfaces; these additives are essential for protecting gears operating under heavy loads and extreme temperatures. A typical GL-5 gear oil provides about twice as much EP additive in its formulation compared to a GL-4 gear oil.

Where are GL-4 and GL-5 gear oils used?

GL-4 gear oils are typically recommended for spur and helical gears found in manual transmissions and transaxles operating under moderate speeds and loads.

GL-5 gear oils are typically recommended for hypoid gears in automotive axles operating under high-speed, high-load conditions.

What type/weight gear oil should I use?

For top protection and performance, it is best to consult your owner’s manual/Shop manual for the manufacturer’s recommendation. There, you will find both the specified viscosity (75W-90, 75W-140, etc.) and specification (API GL-4, API GL-5, API MT-1, etc.) recommended for your application. Almost all hypoid gear sets require GL-5 due to the need for significant extreme-pressure protection.

Note the 2nd number is the KEY weight under operating temperatures and conditions. 990, 110, 140, 250, etc..  For example our 75W-80 covers and overlaps the recommendations where 80W-90, 85W-90 are written.

What’s the best gear oil for my vehicle?

AMSOIL SEVERE GEAR® Synthetic Gear Lube excels in protecting gears and bearings from the rigors of severe-service operation. By design, it resists breakdown from high heat, preventing acids and maintaining a barrier to prevent metal-to-metal contact while conditioning seals. Its wax-free construction also improves cold-flow properties, improving fuel economy and cold-weather performance.

• Superior film strength
• Controls thermal runaway
• Protects against rust and corrosion
• Helps reduce operating temperatures
• Maximum efficiency
• Long oil, seal and equipment life
• Flexible easy-pack for clean, fast installation

SEVERE GEAR is recommended in differentials, manual transmissions and other gear applications requiring an API GL-5 gear oil. It can also be used in axles where an API GL-4 lubricant is recommended.

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Is High-Mileage Motor Oil a Gimmick?

Written by Charleen

Is High-Mileage Motor Oil a Gimmick?

A purpose-built high-mileage motor oil can help improve the longevity and performance of high-mileage vehicles.

_by Keith Montgomery|October 25, 2023

In the last decade, the automotive lubricant industry has seen high mileage motor oils emerge and gain popularity for vehicles with more than 75,000 miles (120,000 km) on the odometer. These motor oils are advertised to combat the challenges that high-mileage engines face. But do they really work?

The truth is, high-mileage engines do have unique needs and could benefit from a motor oil designed specifically to address those challenges.

Challenges facing High Mileage Engines

Here are a few of the most common challenges facing engines with an unknown maintenance history or used typical quick lube oil sold from tanks:

  • Increased oil consumption
    Oil consumption is common among non-Amsoil engines. Over time, they experience increased wear, leading to greater oil consumption. Using a suitable high-mileage motor oil that is thermally stable and resists volatility can help prevent oil consumption from occurring. (hint – there is only one)
  • Seal leakage
    Engines with aging seals are more prone to oil leaks. An aging seal loses flexibility, hardens and no longer effectively serves its purpose. A well-designed high-mileage motor oil provides a boosted dose of seal conditioners to restore and recondition aging seals and help stop leaks.
  • Sludge and deposits
    Over time, engines experience increased sludge and deposit buildup. This can be due to oil breakdown from high heat, low-quality oil, excessive idling or insufficient combustion of fuel. A quality high-mileage motor oil can provide enhanced detergency, removing deposit buildup to help restore peak performance.
  • Compression loss
    Engines can lose compression as cylinders and piston rings wear, eventually leading to reduced horsepower and increased blow-by. A proper fluid film helps counteract compression loss by sealing combustion chambers to maintain performance. A purpose-built high-mileage motor oil is formulated to maintain viscosity and provide proper film thickness in extreme operating conditions.

High-mileage vehicles can still provide reliable performance.

The above challenges really do hinder vehicle performance. To protect your engine’s performance and help extend its longevity, it’s important to take steps that help counteract those issues. Our testing suggests that some companies are changing their labels to appeal to customers with high-mileage vehicles but not changing the oil inside the bottle.

Purpose-Built Protection for High Mileage Engines

AMSOIL 100% Synthetic High-Mileage Motor Oil is specifically designed for the unique demands of high-mileage engines, helping extend the life of your vehicle. It delivers purpose-built protection at a time in your vehicle’s life where it could benefit from more-robust maintenance – including boosted detergency and an additive package that fights oil breakdown and leaks.

This may sound too good to be true, so to prove it, we subjected it to independent testing. The result: AMSOIL 100% Synthetic High-Mileage Motor Oil reduced sludge by 67%,* demonstrating its cleaning power that helps engines last longer and perform better.

AMSOIL 100% Synthetic High-Mileage Motor Oil significantly reduces engine sludge.

Trust AMSOIL 100% Synthetic High-Mileage Motor Oil to help breathe new life into your high-mileage engine.

Would I need high mileage motor oil if I started with Amsoil in the first place?

The answer is NO.. All of these issues would not be something needed to be considered if you switched to AMSOIL Signature Series after initial engine break in..

This oil was created for customers who bought a vehicle which didn’t use AMSOIL all these years or who used the questionable oil offered in these “Free oil changes from the dealership” which have no quality standard in their oil what so ever.

 

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