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Automotive Gear Lubricants-  AHEAD OF THE CURVE

AMSOIL Introduces Its New Line of Synthetic Gear Lubes

Brought to you by highly experienced Truck and Automotive Engineers and Lubrication Specialists. We have 27 years experience engineering and testing cars, trucks, engines, chassis components and systems, powertains and lubricants and we will put our extensive knowledge to use for you.

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We have packed this website with useful information that will help you to make an informed decision regarding your choice of lubrication and filtration products for your vehicles and equipment.  

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The automotive industry is not static. With technology constantly improving, vehicle and engine designs change. Today's vehicle line-up is vastly different than it was 10 years ago, with SUVs and trucks representing the fastest growing segment of the U.S. automotive market. In addition, the industry is moving away from front wheel drive vehicles, and rear wheel drive vehicles are making a strong comeback. The rapidly changing and diversifying vehicle market requires new and improved gear lubricants.

What has changed?

Modern vehicles are designed with more horsepower and torque than in years past, allowing them to haul and tow heavier and heavier loads. This results in higher gear loading and hotter running differentials. In addition, factors such as increased interior space and lower floor boards push axles higher into the vehicle's body, reducing air flow and increasing heat. The closer proximity of the axles to the exhaust system also effectively raises heat, while more aerodynamic body styles and air dams result in restricted airflow to the differentials.

A number of factors causes SUV, pickup truck and van gears to operate under more severe conditions than over-the-road trucks, contributing to increased temperatures, higher gear loading and shorter drain intervals. First, these vehicles have smaller gear that must handle higher loads per square inch of surface area. Second, their smaller sump sizes (and lower volume of gear lube) cannot dissipate heat as well as larger sump sizes. Third, air flow is significantly reduced compared to over-the-road trucks. Fourth, these vehicles are subject to more frequent stop and go driving conditions and are more susceptible to moisture from condensation due to varying temperature fluctuations.

The AMSOIL Solution

In order to optimize its gear lubes for modern applications, AMSOIL has updated its gear lube formulations.

SEVERE GEAR Synthetic Extreme Pressure Gear Lubes (75W-90 & 75W-140)

Specially formulated for severe duty applications, AMSOIL SEVERE GEARynthetic Extreme Pressure Gear Lubes are excellent for vehicles that experience towing, hauling, steep hill driving, commercial use, racing, off-road use, rapid acceleration, stop and go driving and high ambient temperatures. AMSOIL SEVERE GEARGear Lubes are formulated with increased levels of premium quality additives, allowing improved limited-slip and locking differential performance. And with high viscosity indices, SEVERE GEAR Gear Lubes provide an extra level of protection at high temperatures. Extra additives provide additional insurance against wear in case of a lubricant film breach. These additives provide an iron sulfide barrier coating that effectively prevents micro-welding that leads to heat and friction. This allows AMSOIL SEVERE GEARGear Lubes to prevent thermal runaway, a phenomenon caused by a lubricant's inability to control friction and increased heat under high-stress conditions! By preventing thermal runaway, AMSOIL SEVERE GEARGear Lubes inhibit component damage and rapid lubricant degradation.

SEVERE GEAR Synthetic 75W-90 Gear Lube (SVG) replaces Series 2000 Synthetic 75W-90 Gear Lube (TGR).

SEVERE GEAR Synthetic 75W-140 Gear Lube (SVO) replaces Series 2000 Synthetic 75W-140 Gear Lube (TGO).

Long Life Synthetic Gear Lubes (75W-90 and 80W-140)

AMSOIL Long Life Synthetic Gear Lubes are formulated with new and enhanced additives designed specifically for extended drain intervals of up to 500,000 miles in over-the-road trucks.

Long Life Synthetic Gear Lubes are engineered to protect gears better than conventional gear oils, resisting acid, carbon and varnish formation and oxidative breakdown. Their superior shear stability allow them to maintain their viscosity during extended service. The enhanced 80W-140 formulation replaces the former 85W-140 formulation, allowing a greater operating range and improved cold temperature performance.

AMSOIL Long Life Synthetic Gear Lubes are available in five gallon buckets, excellent for use with lube dispensing pumps.

Long Life Synthetic 75W-90 Gear Lube (FGR) replaces Synthetic 75W-90 Gear Lube (AGR).

Long Life Synthetic 80W-140 Gear Lube (FGO) replaces Synthetic 85W-140 Gear Lube (AGO).


80W-90 Synthetic Gear Lube

The 80W-90 gear lube market is mineral oil based. New reformulated AMSOIL 80W-90 Synthetic Gear Lube is designed as a high quality synthetic replacement for mineral gear oils. It is a multifunctional product designed to surpass the requirements of equipment and automotive applications calling for an SAE 80W-90 viscosity grade. Its naturally high viscosity index and shear stable construction provide improved cold temperature performance, while extreme pressure additives provide excellent protection for gears and bearings. AMSOIL 80W-90 Synthetic Gear Lube is competitively priced, making it an excellent choice for cost-conscious customers.          

The most common SAE viscosity grade gear lube used in production cars and light trucks is 80W-90.  75W-90 is also a very common viscosity grade gear lube. If your vehicle specifies 80W-90, as many production vehicles do, you can certainly use a 75W-90. There is very little difference between the two. According to SAE J306 specification the maximum temperature for a viscosity of 150,000 centipoise for a 75W is minus 40 deg. C. while the value for an 80W is minus 26 deg. C.  This simply means that the 75W is going to flow slightly better under colder temperatures than the 80W will, but nothing that you will ever be able to detect without very specialized test equipment.  Both viscosity gear lubes will protect equally well and are both 90 weight gear lubes at normal operating temperatures. 

Many light, medium and heavy-duty trucks will specify an 85W-140. In this case you can use an 85W-140 or a 75W-140. The differences are in cold weather flow properties.  The 75W-140 is going to flow slightly better than the 85W-140 in cold weather until the gear lube warms up in which case they will both perform as a 140 weight gear lube. Many synthetic gear lubes will show SAE grades of 75W because of their excellent low temperature characteristics. 

Synthetic Gear Lubes 

There are several manufacturers are using a synthetic 75W-140 gear lube in some light trucks and performance vehicles while a few also use a synthetic 75W-90 in some high performance cars.  One of the first production applications of a 75W-140 synthetic gear lube I can remember in a production light truck was in a very performance model that was having heat related problems in the rear axle that was causing the plastic housing of the 3-channel anti-lock system (ABS) sensor located in the differential housing to overheat and distort. 

In a typical ABS system there is a toothed sensor at each wheel that measures wheel speeds and compares them using sophisticated computer technology and can determine which wheel or wheels is locked up and then send a signal to the ABS unit to modulate brake pressure.  This is called a 4-channel system.  A 3-channel ABS system is a less costly type of system and only has one sensor at the rear differential and one at each front wheel, thus the name 3-channel ABS system. The only way to solve the problem was to use a synthetic 75W-140 gear lube in the axle. The synthetic gear lube lowered the temperatures significantly and eliminated the problem, as well as provided for increased performance and durability of the gear set and axle bearings.  You will see that several manufacturers are now using and specifying synthetic gear lube for axles, especially in the rear axles of trucks. The synthetic gear lube is used for a reason. A manufacturer is generally not going to use a higher performance and more costly gear lube unless it is necessary to solve a specific problem or improve performance or durability issues.  The synthetic gear lubes that are used as a factory fill are superior to petroleum gear lubes. 

When it comes time to change the factory fill synthetic gear lube I recommend purchasing one of the premium quality synthetic gear lubes manufactured by AMSOIL INC.  The performance is superior and the cost is significantly less that you will pay by purchasing it from the dealership and the specifications state that in non-commercial applications their gear lubes do not require changing (unless severely contaminated by dirt of water). For commercial applications the change interval specification is five times that of a petroleum gear lube. They offer the regular synthetic and the Severe Gear synthetic which is a higher performance formulation. I know of many professional racing teams that use the Severe Gear Synthetic Gear Lubes.  

If your vehicle originally came with a petroleum gear lube I recommend upgrading to a premium quality synthetic gear lube.  Synthetic gear lubes operate at different temperature ranges in relation to viscosity than petroleum gear lubes do.  This allows for one gear lube to cover a wide range of operational, temperature and load conditions from extreme cold to extreme heat.  PAO are the most commonly used base stocks for synthetic gear lubes for automotive applications and are formulated without any viscosity index improvers (VI) since PAO have a natural high viscosity index of the base fluid.  For example, a synthetic 75W-90 gear lube will flow to temperatures as low as minus 40 deg. C. while a petroleum based 80W-90 gear lubricant flow is retarded at these very low temperatures. 

Synthetic gear lubes are also is much more shear stable. A petroleum multi-viscosity gear lube will contain VI in order to meet the viscosity-spread requirements while the synthetic multi-viscosity gear lube will not. In a test of two different trucks using 75W-90 petroleum and synthetic gear lubes, the truck with the petroleum gear lube actually heared out of grade, lowering the viscosity considerably. The gears from this test showed excessive wear indicative of low viscosity.  By comparison, the truck with the synthetic based PAO showed very little shear loss and showed acceptable performance at the end of the test . Synthetic gear lubes are also superior in the areas of oxidative and thermal stability and there is significant data supporting this fact from both axle manufacturers and synthetic oil manufacturers, however it is not my intention to review the data in this book. Synthetic gear lubes will also allow for a reduction in lube temperature, easier shifting in automotive manual transmissions and gearboxes such as on motorcycles and also show a significant improvement in cold weather shifting performance 

Friction Modifiers 

It is also important to note that manufacturers also specify a friction modifier, typically 4-oz., to be added when gear lube is replaced in an axle that has a factory (or aftermarket) limited slip differential.  With some synthetic gear lubricants this is typically not the case. As discussed previously, synthetic lubricants are not more lippery than petroleum gear lubricants. I recently had a customer that was told he needed to use twice as much friction modifier with a synthetic gear lube due to the increased lipperiness of synthetics. Again, this is not true. I know of some premium quality synthetic gear lubricants that do not require any friction modifiers to be added with limited slip differentials. Check the gear lube manufacturers specification to determine if a friction modifier is required before putting it in. It will be of no benefit if you install it when it is not needed. The best way to determine if a friction modifier is required is to, after installing the synthetic gear lube in a limed slip axle, go out and drive the vehicle as you normally would but also be sure to make several tight right and left turns, or find a location where you can safely and slowly drive in a figure 8 pattern for a minimum of eight to ten repetitions.   If you notice any chatter on turns then you most likely need a friction modifier and you can take out the differential filler plug and add it very easily. If you do not get any chatter then you do not need friction modifier. 

Extreme Pressure Additives and Performance 

Another important aspect of gear lubes to consider is extreme pressure (EP) performance and additives. Both petroleum and synthetic gear lubricants utilize EP additives where film strength and extreme pressure performance are needed to combat high shock loading of the gears.  Sulfur, phosphorus and/or chlorine based additives are often used, although chlorine is not fully effective or may cause corrosion concerns where water is present .  The most common EP additives are a sulfur-phosphorus combination in automotive gear lubes. 

Extreme pressure additives are activated by heat rather than by pressure.  When activated by heat they then chemically react with the metal surfaces on the gears to form a film that wears or polishes off slowly rather than allowing the mating surfaces to weld together causing destruction of the gears, bearings and even axle shafts once metal particles and fragments are loose inside the axle housing and are circulated by the gear lube. 

Note that it takes time in service for this protective film to develop but once that it has developed it has a lower shear strength than the metal used for the gears and thus reduces friction and heat. These sulfur and phosphorus compounds can also tend to be corrosive to non-ferrous parts. There are different GL ratings for different type of gear lubes and applications. Applications requiring a gear lube which is friendly to non-ferrous parts  (such as in marine outboard and stern drive lower unit gears and certain manual transmissions, which use aluminum or magnesium cases and other non-ferrous bushings and components) typically will specify a GL-4 rated gear lube which has a different EP additive chemistry and is compatible with the non-ferrous components.  

The GL ratings are specified by the API and are as follows: 

GL-1:  Specified for automotive spiral-bevel and worm gear axles and some manual transmissions subject to mild service and that can be sensitive to some EP additives.  These lubes usually contain rust and oxidation inhibitors, defoamants and pour point depressants but do not contain any EP additives or friction modifiers. 

GL-2:  Specified for automotive worm gear axles that are subject to more severe service than that which is covered under the GL-1 specification. 

GL-3:  Specified for manual transmissions and spiral-bevel axles operating under moderately severe service. 

GL-4: Specified for hypoid gear service without shock loading, but still moderate to severe service (high speed/low torque and low speed/high torque).  These lubes may be used in manual transmissions and transaxles where EP additives are acceptable and typically contain a different zinc additive combination. This classification is still commonly used, but is also obsolete. It is also a commonly specified for marine outboard and stern drive lower unit gears and bearings where the manufacturer specifies GL-4 rated performance.  GL-4 rates lubes are not recommended as a replacement for GL-5 rated lubes. GL-5 rated lubes shows significantly better anti-wear (anti-score) properties than GL-4 rated oils under similar service conditions 

GL-5:  Specified for hypoid gears under shock loading and severe service operating conditions used in cars and trucks. This is the most common and widely used specification today.  These lubes have a high level of EP additives and, depending on the manufacturer and formulation, could be mildly corrosive to non-ferrous parts in certain applications. 

GL-6:  This classification is obsolete and/or was never formally adopted by the API, although I have seen some racing type gear lubes advertised as high-performance GL-6.  It is more than likely advertised this way for marketing purposes. 

API MT-1:  Specified for manual transmissions that do not have synchronizers. The oxidation level and thermal stability is higher than GL-1, GL-4 and GL-5. 

MIL-PRE-2150E:  Specified by the military for automotive gear lubes. It combines the requirements of API GL-5 and MT-1. 

Note that in although the previous lubricant specifications have generally provided satisfactory levels of performance for current automotive gear units, some difficulties have been experienced in low-temperature service because operating temperatures are not always high enough to fully activate the various EP agents.  This disadvantage is usually overcome by using a higher dosage level of additive in lubricants intended specifically for arctic-like service.  In cases such as arctic-like service synthetic gear lubricants will be a major improvement over petroleum based gear lubricants.  I know of some auto manufacturers that install synthetic lubricants in vehicles destined for areas that experience extended arctic weather conditions.

AMSOIL Severe Gear gear lube outperforms every conventional, synthetic and performance gear lube on the market. Dale Earnhart Inc. has recently tested this gear lube in the differentials of their race cars and it is the ONLY gear lube they have tested with has solved their performance problems. AMSOIL reported that one of the mechanics on the race team remembered AMSOIL after they exhausted testing other gear lubes that all failed, they then tested the AMSOIL Severe Gear lube and it solved their problem. Stay tuned for future developments on this.

SEVERE GEAR Synthetic Extreme Pressure (EP) 75W-140 Lubricant Formulated for the severe operating conditions of today's pick-up trucks, SUVs, heavy equipment and other hard working vehicles.

AMSOIL Severe Gear Synthetic Extreme Pressure (EP) Lubricants are premium grade lubricants specifically engineered for maximum performance in severe duty applications. These state-of-the-art AMSOIL formulations feature an exclusive blend of high viscosity, shear stable synthetic base oils and an extra treatment of high-performance additives. AMSOIL Severe Gear Synthetic EP Lubricants maintain their viscosity for long-lasting protection against metal-to-metal contact. The proprietary AMSOIL additives form an iron-sulfide barrier coating on gear surfaces, providing the ultimate line of defense against wear, pitting and scoring. AMSOIL Severe Gear lubricants prevent "thermal runaway" - a phenomenon caused by a lubricant's inability to control friction and increased heat under high-stress conditions. By preventing thermal runaway, AMSOIL Severe Gear Synthetic EP Lubricants inhibit rapid lubricant degradation and component damage. Equipment runs better and lasts longer with AMSOIL Severe Gear Synthetic EP Lubricants. Use in differentials, manual transmissions or other gear applications where one or more of the following standards are specified: API GL-5 & MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037) for 250,000 miles, Mack GO-J, Arvin/Meritor 0-76N (75W-90) & 0-76M (75W-140), plus hypoid gear oil specifications from all foreign and domestic manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in rear axles where API Service GL-4 lubricant is recommended. Product Code: SVO Performance AMSOIL SEVERE GEARprovides performance beyond that possible with conventional gear oil. These AMSOIL custom products offer superior gear and bearing protection, better friction and heat reduction, increased efficiency and extended service life. Temperature Extremes AMSOIL SEVERE GEAREP lubricants excel in hot and cold temperature extremes. By design, they resist breakdown from high heat, preventing acids and carbon/varnish formation. Their waxfree construction also improves cold flow properties, improving fuel economy and cold weather shifting. Applications AMSOIL SEVERE GEARynthetic EP Lubricants are excellent for severe applications, such as towing, hauling, steep hill driving, commercial use, plowing, racing, off-road use, rapid acceleration, frequent stop-and-go operation and high ambient temperatures. Higher horsepower, towing and hauling capabilities of modern vehicles make turbo diesel pick-ups, SUVs, vans and delivery/utility vehicles especially prone to severe service. Other severe duty vehicles include light, medium and heavy-duty trucks, busses, heavy equipment, 4X4s, tow trucks, race cars, tractors, and motorhomes. TYPICAL TECHNICAL PROPERTIES AMSOIL SEVERE GEARynthetic Extreme Pressure (EP) SAE 75W-140 Lubricant Kinematic Viscosity @ 100C, cSt (ASTM D-445) 25.5 Kinematic Viscosity @ 40C, cst (ASTM D-445) 183.9 Viscosity Index 173 Brookfield Viscosity, cP (150,000 Max) @-40C 120, 200 Flash Point, C (F) (ASTM D-92) 150C Min. 210 (410) Pour Point, C (F) (ASTM D-97) -48(-54) Copper Corrosion (ASTM D-130) 1b Max @ 121 C (250F) / 3hr 1b Falex Procedure B (ASTM D-3233) (failure load, lbf.) 1500 Foam Stability (ASTM D-892) (20/50/20 maximum) 0/0/0 For product service life in differentials, consult your owner's manual or the Original Equipment Manufacturer (OEM) to establish the application, NORMAL or SEVERE.   NORMAL SEVERE Cars, SUV, Light & Medium Duty Trucks Drain at 100,000 miles of service or according to the owner's manual, whichever is longer Drain at 50,000 miles of service or according to the owner's manual, whichever is longer Heavy Duty Class, 8 Truck, Commercial Equipment Follow the OEM drain interval (miles or hours) for synthetic oil up to 250,000 miles. Otherwise, drain at twice the OEM interval for conventional oil. Follow the OEM drain interval (miles or hours) for synthetic oil. Otherwise, drain at twice the OEM interval for conventional oil. For product service life in non-differential applications, consult owner's manual or the OEM for either normal or severe synthetic oil service intervals. Where service intervals are unavailable, drain at twice the interval for conventional oil. Gear oils should be changed more frequently when operating vehicles or equipment in dusty or dirty conditions unless the gear system is properly sealed and equipped with membrane type breathers. AMSOIL SEVERE GEAR (75W-140) replaces competitors' 75W-140, 80W-140 and 85W-140 viscosity grades. AMSOIL SEVERE GEAR is compatible with conventional gear oils, however mixing oils reduces the benefits and nullifies the extended service life recommendations. AMSOIL SEVERE GEAR is compatible with most limited slip differentials. If limited slip differential chatter occurs, add AMSOIL Slip-Lock friction modifier additive. Note: AMSOIL does not support extended drain intervals where water contamination occurs. Check and service the gear oil frequently when water contamination is possible. AMSOIL has optimized gear lube performance for specific operating conditions. However, AMSOIL gear lubes are multi-functional and may be used in many different applications. This chart conveys the best AMSOIL recommendation based on product design and operating environment. First row product recommendations offer superior performance in the respective applications. Second row product recommendations offer excellent performance in the respective applications. The third row is exclusive to SAE 80W-90 viscosity. AMSOIL SEVERE GEAR75W-90 (SVG) and 75W-140 (SVO) synthetic gear lubes have a performance emphasis on the extreme pressure and high heat of today vehicle differentials. AMSOIL Long Life 75W-90 (FGR) and 80W-140 (FGO) synthetic gear lubes have a performance emphasis on 500,000 mile extended drain intervals associated with larger sumps and lower operating temperatures of over-the-road truck differentials. AMSOIL 75W-90 synthetic gear lubes will outperform conventional 80W-90 gear oils in all applications and may be used as a replacement.AMSOIL offers 80W-90 (AGL) synthetic gear lube for those customers requiring this specific viscosity grade.

SEVERE GEAR Synthetic Extreme Pressure (EP) 75W-90 Lubricant Formulated for the severe operating conditions of today's pick-up trucks, SUVs, heavy equipment and other hard working vehicles. AMSOIL Severe Gear Synthetic Extreme Pressure (EP) Lubricants are premium grade lubricants specifically engineered for maximum performance in severe duty applications. These state-of-the-art AMSOIL formulations feature an exclusive blend of high viscosity, shear stable synthetic base oils and an extra treatment of high-performance additives. AMSOIL Severe Gear Synthetic EP Lubricants maintain their viscosity for long-lasting protection against metal-to-metal contact. The proprietary AMSOIL additives form an iron-sulfide barrier coating on gear surfaces, providing the ultimate line of defense against wear, pitting and scoring. AMSOIL Severe Gear lubricants prevent "thermal runaway" - a phenomenon caused by a lubricant's inability to control friction and increased heat under high-stress conditions. By preventing thermal runaway, AMSOIL Severe Gear Synthetic EP Lubricants inhibit rapid lubricant degradation and component damage. Equipment runs better and lasts longer with AMSOIL Severe Gear Synthetic EP Lubricants. Use in differentials, manual transmissions or other gear applications where one or more of the following standards are specified: API GL-5 & MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037) for 250,000 miles, Mack GO-J, Arvin/Meritor 0-76N (75W-90) & 0-76M (75W-140), plus hypoid gear oil specifications from all foreign and domestic manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in rear axles where API Service GL-4 lubricant is recommended. Product Code: SVG Performance AMSOIL SEVERE GEARprovides performance beyond that possible with conventional gear oil. These AMSOIL custom products offer superior gear and bearing protection, better friction and heat reduction, increased efficiency and extended service life. Temperature Extremes AMSOIL SEVERE GEAREP lubricants excel in hot and cold temperature extremes. By design, they resist breakdown from high heat, preventing acids and carbon/varnish formation. Their waxfree construction also improves cold flow properties, improving fuel economy and cold weather shifting. Applications AMSOIL SEVERE GEARynthetic EP Lubricants are excellent for severe applications, such as towing, hauling, steep hill driving, commercial use, plowing, racing, off-road use, rapid acceleration, frequent stop-and-go operation and high ambient temperatures. Higher horsepower, towing and hauling capabilities of modern vehicles make turbo diesel pick-ups, SUVs, vans and delivery/utility vehicles especially prone to severe service. Other severe duty vehicles include light, medium and heavy-duty trucks, busses, heavy equipment, 4X4s, tow trucks, race cars, tractors, and motorhomes. TYPICAL TECHNICAL PROPERTIES AMSOIL SEVERE GEARynthetic Extreme Pressure (EP) SAE 75W-90 Lubricant Kinematic Viscosity @ 100C, cSt (ASTM D-445) 16.6 Kinematic Viscosity @ 40C, cst (ASTM D-445) 115.0 Viscosity Index 156 Brookfield Viscosity, cP (150,000 Max) @-40C 87,462 Flash Point, C (F) (ASTM D-92) 150C Min. 218 (424) Pour Point, C (F) (ASTM D-97) -51(-60) Copper Corrosion (ASTM D-130) 1b Max @ 121 C (250F) / 3hr 1b Falex Procedure B (ASTM D-3233) (failure load, lbf.) 1500 Foam Stability (ASTM D-892) (20/50/20 maximum) 0/0/0 For product service life in differentials, consult your owner's manual or the Original Equipment Manufacturer (OEM) to establish the application, NORMAL or SEVERE.   NORMAL SEVERE Cars, SUV, Light & Medium Duty Trucks Drain at 100,000 miles of service or according to the owner's manual, whichever is longer Drain at 50,000 miles of service or according to the owner's manual, whichever is longer Heavy Duty Class, 8 Truck, Commercial Equipment Follow the OEM drain interval (miles or hours) for synthetic oil up to 250,000 miles. Otherwise, drain at twice the OEM interval for conventional oil. Follow the OEM drain interval (miles or hours) for synthetic oil. Otherwise, drain at twice the OEM interval for conventional oil. For product service life in non-differential applications, consult owner's manual or the OEM for either normal or severe synthetic oil service intervals. Where service intervals are unavailable, drain at twice the interval for conventional oil. Gear oils should be changed more frequently when operating vehicles or equipment in dusty or dirty conditions unless the gear system is properly sealed and equipped with membrane type breathers. AMSOIL SEVERE GEAR (75W-90) replaces competitors' 75W-90 and 80W-90 viscosity grades. AMSOIL SEVERE GEAR is compatible with conventional gear oils, however mixing oils reduces the benefits and nullifies the extended service life recommendations. AMSOIL SEVERE GEAR is compatible with most limited slip differentials. If limited slip differential chatter occurs, add AMSOIL Slip-Lock friction modifier additive. Note: AMSOIL does not support extended drain intervals where water contamination occurs. Check and service the gear oil frequently when water contamination is possible. AMSOIL has optimized gear lube performance for specific operating conditions. However, AMSOIL gear lubes are multi-functional and may be used in many different applications. This chart conveys the best AMSOIL recommendation based on product design and operating environment. First row product recommendations offer superior performance in the respective applications. Second row product recommendations offer excellent performance in the respective applications. The third row is exclusive to SAE 80W-90 viscosity. AMSOIL SEVERE GEAR75W-90 (SVG) and 75W-140 (SVO) synthetic gear lubes have a performance emphasis on the extreme pressure and high heat of today vehicle differentials. AMSOIL Long Life 75W-90 (FGR) and 80W-140 (FGO) synthetic gear lubes have a performance emphasis on 500,000 mile extended drain intervals associated with larger sumps and lower operating temperatures of over-the-road truck differentials. AMSOIL 75W-90 synthetic gear lubes will outperform conventional 80W-90 gear oils in all applications and may be used as a replacement.AMSOIL offers 80W-90 (AGL) synthetic gear lube for those customers requiring this specific viscosity grade.