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

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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No Fear and Loathing at the Mint 400

No Fear and Loathing at the Mint 400

“In some circles, the Mint 400 is a far, far better thing than the Super Bowl, the Kentucky Derby and the Lower Oakland Roller Derby Finals all rolled into one. This race attracts a special breed…”  – Hunter S. Thompson

In 1971, author Hunter S. Thompson wrote his famous article “Fear and Loathing in Las Vegas” while covering the Mint 400 for Sports Illustrated. Thompson’s article was later adapted into a novel and then into a film starring Johnny Depp and Benicio Del Toro, signifying the Mint 400’s relevance to American pop culture.

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The Mint 400 started in 1967 near Las Vegas as a public relations event to promote the Mint Hotel’s annual deer hunt. Race organizers sent two matching dune buggies 600 miles through the desert from the Mint Hotel to the Sahara Hotel in Lake Tahoe, Calif. The event because famous overnight, with national television coverage drawing the attention of race fans across the country.

Some of the “special breeds” who have competed in this event include Al and Bobby Unser; Rick Mears; Mickey Thompson; actors Steve McQueen and Patrick Dempsey; and comedian Jay Leno.

AMSOIL racers to take to the desert

Coming off an impressive seventh-place finish at the King of the Hammers UTV race last month, two-time Mint 400 champion Bryce Menzies is looking to do it again in this year’s Trick Truck class. His fellow #TeamAMSOIL racer Brad Lovell is also looking to keep the momentum going following a second-place finish at last month’s King of the Hammers EMC. Lovell, who took second in the Vintage Open Class at last year’s Mint 400, will be competing in his first ever 6100 race.

Prior to racing on Friday, Lovell’s pit crew will participate in the Method Race Wheels Pit Crew Challenge along Fremont Street on Thursday evening.

Stop by the AMSOIL booth

AMSOIL will be located on Fremont Street throughout all the pre-race events. Be sure to stop by and pick up your exclusive Runs on Freedom™ bandana. Fill out our survey on Friday, March 8 for a chance to win the fender from Lovell’s new 6100 truck following the race.

On Thursday and Friday, Menzies’ UTV from King of the Hammers will be on display. Lovell’s Bronco will be displayed Thursday and his new 6100 on Friday. Both Menzies and Lovell will be in the booth Friday at 2 p.m. local time signing autographs for fans.

Buy two SEVERE GEAR® easy-packs, get one free

We’re also offering a special promotion as part of our Mint 400 partnership. Buy two AMSOIL SEVERE GEAR Synthetic Gear Lube easy-packs and get one free. It’s the same gear lube Menzies and Lovell trust in their race vehicles.

Find more information on the promotion here.

As always, tune into our social media channels for updates throughout the race. The week kicks off Wednesday, March 6 in Las Vegas. Check out the complete schedule of Mint 400 events here.

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We’ll see you at the races!