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At an education session last December for ASTM, Chris May of Imperial Oil in Sarnia, Canada, gave an excellent presentation on the history of the SAE Viscosity Classification System. He traced the birth and evolution of engine oil viscosity classification, now known as SAE J300.

First issued in 1911 and modified more than 20 times over the last 96 years, the Viscosity Classification System has evolved from a comprehensive descriptive system (1923) including physical tests for color, flash point, fire point, Conradson carbon residue, copper corrosion and pour point; to a sophisticated standard (SAE J300 MAY2004) measuring all aspects of high-shear and low-shear viscometrics – at temperatures from -40 degrees C to 150 C and shear rates from virtually nil to 106 reciprocal seconds. The range of temperatures and shear rates is designed to mimic the range of conditions found in a modern internal combustion engine.

Along the way, temperature ranges, measurement systems and test methodologies changed numerous times. Tests and limits were added and subtracted. Field problems were addressed and changes made to accommodate the lessons learned from these problems. All in all, SAE J300 is a remarkable document which has stood the test of time. The question now is: Can it deliver on the next level of need as proposed by the original equipment manufacturers?

Tracing the Past

The methods used to measure viscosity and the limits placed on viscosity for use in automobile engines were, and continue to be, critical to overall engine performance and customer satisfaction. So what were the viscosity grades of choice over the years, and what forces have been at work to change them?

If we go back to the beginning of the SAE Viscosity Classification System in 1911, automobile engine oils were essentially base stocks that had been dewaxed, and Penn-Grade was the finest available. The viscosity grades were ill-defined and certainly were not multigrade, May noted.

Move forward to 1923 and we have the first defined viscosity grades. There are lots of specification numbers (viscosity grades) we dont see any more. In addition, there are two (020 and 030) which are the first attempts at defining a winter grade. The other significant observation is that there are physical test requirements included. There were classifications issued in 1926 and 1933 which reduced the number of viscosity grades, changed the definition of each grade and which eliminated the physical tests from the 1923 classification. There were still no additives in engine oils except for pour-point depressants, which were first introduced in the late 20s. There were no multi-viscosity engine oils in the market.

The 1940s: Enter Additives

The years from 1933 to 1950 saw no new viscosity classification documents from SAE. In the 1940s the automobile industry introduced its own viscosity classifications for its vehicles, outside the SAE system. Meanwhile, engine oils were still not multi-graded. However, the first modern additive components were introduced. Zinc dialkyl dithiophosphate (ZDDP) was first patented in 1941 as a corrosion inhibitor. Its capabilities as an antiwear agent and antioxidant were quickly recognized. Detergents were also introduced at about the same time. They provided protection against surface deposits in engines operating at high temperatures.

In 1950, May explained, for the first time extrapolated viscosity at 0 degrees F was specified and W grades made their first appearance. While not a big part of the marketplace, multigrade oils began to show up on the forecourt of service stations as the premium product from major marketers. These were based on the use of polymeric viscosity index improvers, such as polyisobutenes and polymethacrylates. Monograde engine oils still were king of the hill.

Throughout the 1950s and early 60s, the multigrade market began to grow. The viscosity grades most often mentioned were SAE 10W-30 and SAE 20W-40, while SAE 10W-40 and 20W-50 were also available. Among monogrades, SAE 30 was still the number one seller. Engine design was still based on SAE 30 viscosity.

New Decade, New Needs

The first emissions rules had been recently introduced (1964) which required the road draft tube to be plugged and the positive crankcase ventilator (PCV) valve to be installed in cars. In California, when cars were resold, they were retrofitted with a PCV valve. This increased the strain on the engine oil, said May. Ashless dispersants were now a part of the additive package for automotive engine oils. They provided protection against low-temperature sludge formation found in gasoline-fueled engines and produced in part by PCV exhaust gas recirculation.

In 1967 the viscosity classification system was called SAE J300a for the first time. There were no substantive changes in limits. However, the first of a new series of test protocols was introduced, the Cold Cranking Simulator (CCS). It was designed to mimic the viscometric requirements of a cranking engine at 0 degrees F. This test really brought the W grades into the running, as they now had a measuring tool all their own.

Multi-vis engine oils began picking up steam at this point, and SAE 10W-40 was the grade growing the fastest. It was touted as the best combination of low-temperature startability and high-temperature protection, and was the premium oil offered by the oil marketers.

In the next 13 years several changes were made to SAE J300. Metrication of test values and limits proceeded, first as soft and later as hard metrication of numbers. Test limits went from 100 and 210 degrees F to 40 and 100 degrees C. Viscosities went from Saybolt Universal Seconds (SUS) to centiStokes (cSt) and centiPoise (cPs). In addition, a new test protocol was introduced to measure low-temperature pumpability. First added to J300b as an appendix, it was officially incorporated in the standards September 1980 rewrite as the Mini-Rotary Viscometer (MRV) test. In addition, the Cold Cranking Simulator now measured viscosity at multiple temperatures, and viscosity numbers finally became viscosity grades.

1982: Wintertime Woes

By 1980, in spite of the fact that fuel economy had become a major issue, monograde engine oils still outsold multigrades, and SAE 30 was the largest viscosity grade in terms of sales volumes. Among multigrades, SAE 10W-40 was the largest seller. SAE 15W-40 wasnt large enough in sales to be reported. However, things were to change drastically over the next few years. Friction modifiers had become a part of the additive package with the advent of fuel-economy testing.

The winters of 1980 and 1981 precipitated one of the most tumultuous times for SAE J300. A number of vehicle failures occurred in the field, their engines damaged because oils failed to pump at frigid temperatures. This was caused by poor low-temperature pumpability that had not been detected by the Mini-Rotary Viscometer procedure. As an interim measure to try to predict such performance, the Stable Pour Point test method was added to SAE J300 APR1984, as well as the use of the Brookfield Viscometer to determine Borderline Pumping Temperature.

In the meantime, ASTM was working on a fix for the MRV. One site of the field failures had been Sioux Falls, S.D. By examining the National Weather Service records for the time period during which the failures occurred, the ASTM task force was able to develop a more representative cooling cycle to predict low-temperature pumpability characteristics of engine oils. This became known generically as the slow-cool borderline pumping temperature procedure. It utilized the same MRV apparatus but with the modified cooling cycle and was a part of SAE J300 JUN87, but only included SAE 5W and 10W grades. The High Temperature, High Shear Viscosity (HTHSV) test also debuted in that edition, which noted that some engine manufacturers specify this test for their engines.

The Fast-moving 90s

In 1985, volume data from the National Petrochemical & Refiners Association showed a huge shift in sales from monograde to multigrade engine oils. SAE 10W-40 was still the most popular grade, primarily for passenger cars. The recently introduced SAE 15W-40 also had grown dramatically and was rapidly becoming the preferred vis grade for heavy-duty engines. SAE J300 JUN89 specified the Borderline Pumping Temperature by the new slow-cool method with an added yield stress limit, and all W grades were now included. In addition, more discussion was presented on the HTHSV test method and its importance to certain OEMs.

NPRAs 1990 volume data showed that SAE 10W-30 had now surpassed SAE 10W-40 and that SAE 5W-30 was growing rapidly, too. SAE 30 had dropped below SAE 15W-40 in volume and was sinking fast. The move to lower-viscosity engine oils was accelerating. Formulations for passenger car engine oils now included friction modifiers to meet more stringent fuel economy requirements.

The first half of the 1990s saw a number of significant changes to SAE J300. FEB91 saw the inclusion of critical limits definitions. In practice, this meant that blenders must aim about 200 cPs below the maximum to attain 95 percent confidence that their oil, if sampled in the field, would actually be less than the limit set. FEB92 included HTHSV limits – but only for the W grades! MAR93 moved the HTHSV limits from the W grades to the non-winter grades and had two limits for SAE 40, depending on the multigrade formulation. (5W and 10W was set at 2.9 cPs minimum, while 15W, 20W and 25W were 3.5 cPs min.) The Cold Cranking Simulator was finally made an official part of J300 when the test method won approval in ASTM.

NPRAs 1995 sales report showed the continued loss of monograde oils and the growth of SAE 5W-30, SAE 10W-30 and SAE 15W-40 in the marketplace. The report was so dismal for monogrades that NPRA didnt bother to break out SAE 30 volume – the number one seller just a few decades before.

Meanwhile, 1993 had seen the introduction of ILSAC GF-1. This was the first engine oil category which included both performance and fuel economy limits in one designation and was steered by the OEMs. GF-1 brought antioxidants into the formulation picture as a supplement to traditional ZDDP. The reduction of phosphorus content to 0.10 percent max in GF-1 meant that there wasnt enough antioxidant without a bit of help from the ashless chemistry side.

A New Century

The last five years of the 20th century brought little change in SAE J300. The limits for CCS were lowered by 5 degrees C to reflect the newer engine technologies which could crank at lower temperatures. Later, MRV limits were also lowered by 5 degrees C in order to insure that oils which would allow cranking would also allow pumping to occur. The fear of the OEMs was always that oils would allow cranking (starting) but could not deliver oil to the engine in a timely manner and cause engine failures.

NPRA volumes for 2000 continued to show the growth of lighter grades and the faltering of the old warriors. SAE 30 dropped to about 65 million gallons while SAE 15W-40 took over as the most commonly produced heavier multi-viscosity oil. SAE 5W-20 made its first independent appearance and SAE 5W-30 and 10W-30 continued to be the largest volume movers. GF-2 and API CH-4 were now part of the scene, steering the light-duty and heavy-duty grades, respectively. Chemistry was getting more expensive as higher-cost antioxidants and friction modifiers became more common in passenger car formulations and antioxidants became a major part of CH-4 chemistry. SAE J300 MAY04 was a cleanup event, removing old references and bringing in the most current nomenclatures.

The picture today? NPRA volumes for 2005 show the virtual demise of mono-grades – Lo, how the mighty have fallen! – and the ascendancy of the lighter-weight multigrades. SAE 5W-20 and 5W-30 are continuing to grow while SAE 10W-30 has leveled off and is beginning to drop. SAE 15W-40 continues to dominate the heavier multi-vis market.

All of this history is a backdrop to the continuing drive by the automakers to squeeze every drop of fuel economy from engine oil, before having to make major concessions in engine design, horsepower and vehicle design. Next month, well look into the ramifications of lower-viscosity engine oils on base stocks, additive chemistries and market acceptance. Stay tuned!

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