Automotive Lubricants



In last months Q&A column, I noted that some really good questions might come from readers before the end of 2019. Well, sure enough, I got a great question about SAE viscosity classification. Its a question that has likely been top of mind for a few marketers and maybe even an oil user or two. The question is, How did we get to the point where viscosity grades seem to be ambiguous or even result in degrading oil quality in order to meet a viscosity grade? Is there a solution, or do we just have to live with it?

SAE J300 says that to qualify for a given winter grade viscosity, an oil must fail at the lower temperature. For example, an SAE 10W-30 oil must fail cold temperature performance tests at the SAE 5W test limits. The readers concern is that when dealing with high-end synthetics, making oils with worse low-temperature properties is difficult, cost prohibitive and seems completely unnecessary.

He also noted that blenders may actually degrade low-temperature performance to make an SAE 10W-30 if the natural viscosity of an oil is SAE 5W-30. He pointed out that the current SAE viscosity system works for conventional base oils but is not effective for certain synthetic base oils, such as polyalphaolefins and esters. Would a better control be through high-temperature, high-shear rate viscosity, since this would be affected by the amount of viscosity modifier in the oil?

In the end, he observed, people dont understand the viscosity system, and they want what they want. Trying to sell an SAE 5W-30 to a customer who wants an SAE 10W-30 is a no-go.

As I usually do, I want to go back to the start of the story to see how we got into the position we are in today. In this case, its a long history. Ive told the story (in parts) on more than one occasion, but lest you think I have a prodigious memory, I want to give credit where credit is due: Chris May, now retired from Imperial Oil, put together an excellent summary of the history of SAE J300 for an ASTM symposium in 2006. Most of the major developments that accompanied the viscosity classification system are covered in his presentation. There are a few important ones that have occurred since then, which Ill note when I get to them.

The first SAE-sponsored viscosity classification was in 1923 and codified what had been done off the cuff since 1911. This classification was actually more than just viscosity. It also identified limits for certain oil properties that impacted performance. Within a short three years, the oil properties were removed and only viscometrics were included. In 1933, the first low-temperature viscosities were introduced based on graphical extrapolation of higher temperature viscosities.

The SAE J300 designation did not appear until 1955 and then only in a recommended practice footnote. Graphical measurement of low-temperature viscometric properties went on until 1967 when the cold cranking simulator was introduced and viscosity limits at 0 degrees Fahrenheit were set. From this point forward, changes started to come more rapidly.

In 1972, soft metrication (converting the official Saybolt Universal Viscosity to metric values) was introduced. In 1973, the first low-temperature, low-shear test development was discussed. That ultimately led to low-temperature pumpability limits. In 1977, the metrication of all test results and temperatures was completed, and recommended practice for low-temperature pumpability would soon follow.

In 1980, SAE J300 SEP80 was introduced with additional requirements. CCS is now multi-temperature with results that are set by temperature for each W grade. The mini-rotary viscometer was introduced with borderline pumping values for each grade. The MRV test temperature was set at 5 degrees Celsius lower than the CCS test temperature for each grade. This was done to make sure the engine, if it could turn over, would be able to get oil to critical parts in time to prevent damage.

Additionally, it was specified that only the lowest W grade should be referred to on the label. This was due to the proliferation of viscosity grades shown on labels. It was confusing to see something like SAE 5W/10W/15W-40 on an oil bottle.

For the next two years, there was an outbreak of low-temperature pumping failures in the field. I was just getting into the J300 jungle and learned a lot about the jargon and the problems. A lot of work was done to try to determine why some oils that met the CCS and MRV requirements of an SAE grade were failing. What came out was the fact that the cooling cycle (how quickly the oil cools) was a crucial factor. One location, Sioux Falls, South Dakota, had undergone a long, slow cooling period, after which many oils that met SAE J300 SEP80 failed.

In addition, base stock properties and refining methods became more involved with the low-temperature performance of engine oils.

Quaker State suffered a major problem when the base stock from one of their sources did not respond to a pour point depressant in the same way that oil from their other sources did. Other companies had to scramble to verify that their PPD worked with the base stocks in their system. In fact, it turned out that API Group II base stocks have a different appetite for PPD than Group I base stocks, causing a lot of fast reformulations.

SAE J300 APR1984 was introduced with an additional test, the stable pour point (a seven-day test), to try to address the problem. The appendix included a Brookfield viscosity test as further backup to catch the low-temperature problem. There was clarification added to further explain the lowest W grade issue. This consisted of a statement that if all requirements were not met for a specific viscosity grade, the oils viscosity was not identifiable. For example, an oil that is supposed to be an SAE 5W-30 that meets the kinematic viscosity at 100 C and the cold crank but doesnt meet the requirement for oil pumpability cannot be called an SAE 5W-30. In fact, it cant be called anything.

SAE J300 JUN87 addressed the borderline pumpability test using the slow cool method (ASTM D4684), which came out of the Sioux Falls study. It was only required on SAE 5W, 10W and 15W. SAE 0W, 20W and 25W continued with the ASTM D3829 method. There was a lot of concern at this point from blenders, since ASTM D4684 is a seven-day test and was not conducive to production blending. SAE 60 was added and, most importantly, HTHSV was mentioned for the first time but with no specification.

Two years later, SAE J300 JUN89 included ASTM D4684 for all SAE W grades, and pumpability was referred to as viscosity/BPT (borderline pumping temperature). The limits for each viscosity grade were set at a temperature 5 C lower than the CCS test temperature. Again, the emphasis was that the oil must pump satisfactorily if the engine was able to crank over and start. The conversation about HTHSV was expanded and test methods referenced.

SAE J300 FEB91 determined that all values were critical, meaning that the oil must meet the set limits. ASTM D3244 determined what precision was needed to assure they were met. The reasoning behind this was that API was sampling oils and found that many were outside established limits due to blending variation. Several states were also sampling oils on the shelf and causing them to be removed if they were out of viscosity limits. The practical impact of this addition was to tighten the viscosity limits for blending.

SAE J300 FEB92 incorporated HTHSV for the first time, but only on SAE W grades. This became an interesting industry debate between the OEMs and the oil companies. I remember Dick Kabel from GM attending an SAE Fuels and Lubricants meeting wearing a lapel button saying 2.9 is Fine. Some of the Ford people were saying 2.7 is Heaven. Privately, GM representatives were saying that field tests of engine oil with 2.6 HTHSV showed no degradation of performance or durability. The oil and additive people were not sure what was correct but begrudgingly went along with the OEMs desire to include HTHSV.

SAE J300 MAR93 was a sort of reversal since the HTHSV limits on SAE W grades were dropped but added to the non-W SAE grades. There were actually two SAE 40 HTHSV limits based on expected application. The SAE 0W, 5W and 10W grades were 2.9 centipoise minimum (light-duty), while the SAE 15W, 20W and 25W were set at 3.7 cP minimum (heavy-duty).

SAE J300 DEC95 changed the low-temperature pumpability limits to 10 C below CCS and raised the maximum viscosity to 60,000 cP. In SAE J300 APR97, there was an adjustment to HTHSV testing to accommodate a different test method. SAE J300 DEC1999 lowered CCS temperatures by 5 C (back to a 5 C difference from BPT) and adjusted viscosity limits to be more representative of engine starting characteristics. J300 MAY2004 cleaned up the various footnotes and appendices and brought the document to its current form.

However, that wasnt the end of the changes. Since 2005, some bureaucratic details have been fixed, including removing the requirement that CCS be a critical value. In 2013, SAE 16 was added, and in 2015, SAE 8 and SAE 12 were added. Viscosity ranges were adjusted to minimize overlap between grades. For the lower viscosity grades where there was overlap in viscosity range, the HTHSV became the deciding factor as to which viscosity grade the oil met.

So the question remains: What do we do about synthetics that have to be de-tuned to meet viscosity limits, and why dont we use HTHSV as the determining limit for setting viscosity grades?

A partial answer is that we do use HTHSV as a final judge to establish viscosity grades. There is a lot of overlap in SAE 8 to SAE 20, so HTHSV is the decider for the lighter viscosities. Perhaps kinematic viscosity at 100 C (also a part of J300) can be used in conjunction with the W grades to establish a similar set of rules.

In any event, the blenders have a difficult choice to make: Do I degrade my synthetic, high-performing product in order to meet viscometric requirements, or do I abandon the traditional SAE 10W-30 viscosity grade? Neither choice is a solution, but both need to be considered. More education for customers is also needed to explain the value of lower viscosity engine oils.

If you havent noticed, J300 is a living, breathing document and continues to change. Sounds like the SAE Engine Oil Viscosity Classification Task Force has more work to do.

Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at steveswedberg

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