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What is the Noack Volatility Test?

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What is TBN?


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AMSOIL Severe Gear Synthetic Gear Lubes Provide Superior Protection Against Thermal Runaway

The Hotter It Gets The Hotter It Gets

Modern turbo diesel pickup trucks, V-10 gasoline pickups and sport utility vehicles (SUVs) and high-horsepower V-8 trucks boast more towing and payload capacities than ever before. In fact, the market has seen a 34 percent increase in engine horsepower over the last decade. In the light truck segment, there has been a 93 percent horsepower increase since 1981. In vehicles such as a fifth-wheel equipped Ford F-350 Super Duty, towing capacities have reached a high of 19,200 lbs. Testing shows that in new axle applications simulating trailer towing at 88 km/h (55 mph) at a 3.5 percent grade, temperatures can reach as high as 188 degrees C (370 degrees F). Differential stress has also increased in limousines, conversion vans, and trucks and cars with modified, high-performance engines.

The extreme loads, pressures and temperatures experienced by modern vehicles place increased stress on gear lubricants that can lead to a serious condition known as thermal runaway. As temperatures in the differential climb upward, gear lubricants tend to lose viscosity, while extreme loads and pressures can break the lubricant film, causing increased metal-to-metal contact and heat. The increased friction and heat, in turn, cause the lubricant to lose further viscosity, which further increases friction and heat. As friction and heat increases, lubricant viscosity decreases. As viscosity decreases, friction and heat continue to spiral upward. The hotter it gets, the hotter it gets. It's a vicious cycle that eventually leads to greatly increased wear and irreparable equipment damage.

AMSOIL Severe Gear Synthetic Extreme Pressure (EP) Gear Lubes feature an exclusive blend of high viscosity, shear stable synthetic base oils and an extra treatment of high-performance additives that provide a highly protective iron sulfide barrier coating on gear surfaces. Severe Gear Synthetic Gear Lubes effectively protect equipment from thermal runaway through superior viscosity protection.

Viscosity Protection

Viscosity is the most important property of a lubricant in its defense against friction and wear. Viscosity correlates to film strength, and it is film strength that keeps moving parts from contacting each other and creating friction, heat and wear. The higher the viscosity of a lubricant, the greater protection it provides. AMSOIL Severe Gear Synthetic Gear Lubes are available in 75W-90, 75W-110, 75W-140, SAE 190 and SAE 250 viscosities, each providing superior protection through superior film strength.

Viscosity Index

As temperatures rise, gear lubricant viscosity and load carrying abilities decrease. A lubricant's viscosity index (VI) indicates its ability to maintain its protective viscosity in high temperature service. The higher a lubricant's VI, the less its viscosity changes in temperature extremes.

The ASTM D-2270 Viscosity Index Test measures a lubricant's viscosity change between 40 degrees C (104 degrees F) and 100 degrees C (212 degrees F). AMSOIL Severe Gear Synthetic 75W-90 Gear Lube provides a high viscosity index , allowing it to protect against thermal runaway by maintaining its superior viscosity protection in high temperature service.

Shear Stability

Many gear lubes are formulated with viscosity index (VI) improvers in order to ensure multi-grade viscosity protection in both hot and cold temperatures. VI improver additives keep lubricants from becoming too thick to flow in cold temperatures and too thin to protect in high temperatures. However, shearing forces within equipment can cause these additives to break down and lose viscosity.

The CEC L-45-A-99 (KRL) 20-Hour Shear Test is a requirement for all automotive gear lubes to ensure they do not shear down and fall below minimum viscosity requirements. The graph shows initial oil viscosity and viscosity following the test, while the shaded area indicates SAE J306 high-temperature viscosity requirements for SAE 90 gear lubes.

(click here to open the PDF version of this article which includes all the graphs)

As seen in the graphs, two gear oils (Lucas 75/90 Synthetic and Royal Purple Max-Gear 75W-90) failed SAE J306 requirements before the shear test began, exceeding the maximum 18.49 cSt initial viscosity requirements for SAE J306. Viscosity measurements following the test revealed that seven gear lubes (Pennzoil Synthetic 75W-90, Mobil 1 Synthetic 75W-90, Pennzoil Gearplus 80W-90, Mopar Synthetic 75W-90 with Mopar LS additive, GM Synthetic Axel 75W-90, Royal Purple Max-Gear 75W-90, Torco SGO Synthetic 75W-90 with Torco Type G LS additive) sheared down below the minimum viscosity requirements for SAE J306. AMSOIL Severe Gear 75W-90 tested in the proper initial viscosity range and retained the highest viscosity of all tested tested oils after the shear test, indicating its superior ability to protect against thermal runaway by maintaining its protection qualities in severe, high shear operating conditions.

The superior viscosity protection, viscosity index and shear stability properties of AMSOIL Severe Gear Synthetic Gear Lubes effectively protect equipment from the devastating effects of thermal runaway. Severe Gear Synthetic 75W-90, 75W-110 and 75W-140 Gear Lubes are ideal for severe-duty applications, including towing hauling, steep hill driving, commercial use, plowing, racing, off-road use, rapid acceleration, frequent stop-and-go operation and high ambient temperatures.

AMSOIL Severe Gear 75W-90 provides superior performance and replaces competing 75W-90 and 80W-90 gear oils. It delivers the best fuel efficiency and cold temperature performance in the Severe Gear line.

AMSOIL Severe Gear 75W-110 provides superior performance and replaces competing 75W-110, 75W-90 and 80W-90 gear oils. It delivers better viscosity protection than Severe Gear 75W-90 and better fuel efficiency than Severe Gear 75W-140.

AMSOIL Severe Gear 75W-140 provides superior performance and replaces competing 75W-140, 80W-140 and 85W-140 gear oils. It is recommended where these viscosities are required by OEMs and where maximum viscosity protection is needed for extreme severe-duty applications.



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Premium AMSOIL Synthetic Motor Oils offer the longest drain intervals on the market, unsurpassed protection and performance that effectively extends equipment life and improved fuel economy, saving customers money at the pump and reducing the nation's dependence on foreign oil.

"AMSOIL INC. warrants that the use of its lubricants will not cause mechanical damage to any mechanically sound equipment when AMSOIL INC. products are used in full compliance with the company's recommendations and instructions."


AMSOIL synthetic motor oils are formulated to surpass engine test specifications, offering protection far greater than competing motor oils for extended drain intervals. Most synthetic oil manufacturers make no claim to extended drain intervals, deferring to the maintenance schedule provided by the vehicle manufacturer. With its unparalleled oil and warranty program, AMSOIL offers consumers unprecedented protection and economics.

Another AMSOIL First

More than 20 years ago, AMSOIL began using the NOACK volatility test as a comparison tool and measurement of quality. Back then, nearly every oil tested side-by-side with AMSOIL synthetic motor oils failed, and those that passed barely squeaked by. Other oil companies paid no attention to NOACK results until Ford Motor Company made it a requirement for service fill oils, validating what AMSOIL had said all along.

THE NOACK Volatility Test
The NOACK Volatility Test determines the evaporation loss of lubricants in high temperature service. The more motor oils vaporize, the thicker and heavier they become, contributing to poor circulation, reduced fuel economy and increased oil consumption, wear and emissions. AMSOIL Synthetic Motor Oil resists high temperature volatization better than other motor oils. AMSOIL Synthetic Motor Oil maintains peak fuel efficiency and reduces oil consumption and emissions.

AMSOIL Now An ISO Certified Manufacturer
AMSOIL recently received ISO 9001:2000 certification of our Quality Management System (QMS). NSF International Strategic Registrations is the registrar that has verified our QMS meets the requirements of the ISO 9001:2000 standard, the most widely utilized quality standard throughout the world for quality management systems. ISO standards are used by over 300,000 companies worldwide setting rigorous standards for businesses, government and industry.

ISO 9001:2000 is applicable to any manufacturing and service organization providing a framework for system development that focuses on the customer, quality system performance and ongoing improvement. AMSOIL received ISO 9001:2000 registration under the scope: synthetic lubricants blending, packaging, and other fulfillment directly associated with lubricant product.

The ISO certification puts AMSOIL in line with some of the most efficient companies in the world. It is further assurance that the products and services AMSOIL provides will continue to maintain the high level of quality the company always demanded.

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