What is Hypoid Gear Oil? (And Other Gear Oil Questions Answered)

We tackle some frequently asked questions about gear oil, including "What is hypoid gear oil?" and other common questions.

December 15, 2020

In this post, we tackle some frequently asked questions about gear oil such as, What is hypoid gear oil? Let’s get started.

What is hypoid gear oil?

Commonly found in axle differentials, hypoid gears are used to transmit power from the driveline to the axle shafts. They are basically spiral bevel gears, where the pinion engages below the centerline of the ring gear. This lowers the driveshaft away from the bottom of the vehicle.

What is hypoid gear oil?

Hypoid gear oil is formulated with extreme-pressure (EP) additives to protect and operate effectively with hypoid gears. AMSOIL SEVERE GEAR® Synthetic Gear Lube offers outstanding protection for hypoid gears.

Can you mix synthetic and regular gear oil?

Yes, synthetic gear oil is generally compatible with conventional gear oil. Mixing synthetic and conventional gear oils may, however, shorten the oil’s life expectancy and reduce its performance benefits. AMSOIL does not support extended drain intervals where oils have been mixed.

Can you use regular automotive gear oil in a marine lower unit?

Yes, as long as it meets the specification in the owner’s manual.

However, for the best protection, it is best to use a gear oil specifically formulated for marine lower unit applications.

Marine lower units are regularly exposed to water, and water contamination of gear oil increases the likelihood of foaming, which disrupts the oil film and leads to wear. Marine gear oils are specially designed to resist foaming and maintain performance when subjected to water contamination.

AMSOIL Synthetic Marine Gear Lube resists foaming and delivers advanced protection against power loss and gear wear, even with up to 15 percent water contamination.*

*Based upon AMSOIL testing of AMSOIL Synthetic Marine Gear Lube 75W-90 in ASTM 3233 and ASTM D892.

What type/weight gear oil should I use?

For top protection and performance, it is best to consult your owner’s 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.

How often should I change gear oil?

Consult your owner’s manual or the original equipment manufacturer (OEM) to establish your application’s operation as either normal or severe, and follow the appropriate guidelines. AMSOIL synthetic gear lubes also provide both normal and severe-service drain interval recommendations, as well as the opportunity to save time and money through extended drain intervals.

What’s the best gear oil for my differential?

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 flows well in cold

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