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OEMs Press for Light-vis Grades

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The SAE J300 Engine Oil Viscosity Classification Task Force met recently to review the status of proposals for new, lower-viscosity grades of engine oil. Interest in these new grades is prompted mainly by the automotive OEMs desire to capture every drop of fuel economy possible through reductions in friction due to the oil. If successful, the introduction of lower-vis grades promises to have lasting impact on engine oil blenders and their base oil suppliers.

SAE J300, the engine oil viscosity classification system, defines the viscosity limits for monograde and multigrade oils that are used worldwide, such as SAE 30, 5W-20, 10W-30, 15W-40 and so on. The lowest W grade today is 0, and 20 is the lowest regular grade.

To assure that they can use lighter-vis oils without fear of excessive engine wear, some automakers have asked SAE for an expanded set of the regular grades, adding SAE 5, 10 and 15. The big issue – and one that the OEMs themselves dont agree on – is how and where to set the high-temperature/high-shear viscosity limits for these new grades. The lowest HTHS viscosity allowed today is 2.6 mPa-s, at 150 degrees C, and some proposals would take this much lower.

Task Force Chairman Chris May of Imperial Oil opened the June 22 meeting in Baltimore with a review of the drivers for these additional grades. Since August 2009, a working group has been assessing the options for extending SAE J300 viscosity grades to oils with HTHS below 2.6 mPa-s.

Last summer, industry stakeholders were polled regarding three options under consideration. Some respondents to the poll advised caution in making any changes to J300 until needs and implications were better defined, May said. Others pointed out that there are already low-viscosity products in the marketplace claiming to meet SAE 0W-10 (including one marketed by a Japanese OEM) and 10W-10 grades that dont exist. This brings urgency for an SAE definition of these new grades.

The proponents for changing SAE J300 generally fall into two groups, May reported:

The first group advocates adding a full slate of viscosity grades below SAE 20, down to 1.4 mPa-s.

Those in the second group want to add only one or perhaps two new grades below SAE 20. SAE J300 can be revisited later to add additional viscosity grades when needed, they point out.

Most respondents to the poll agreed that any new grades should have distinct kinematic viscosity ranges as well as HTHS limits; this would also affect SAE 20 grade definitions. Most also appeared comfortable with HTHS increments of 0.3 mPa-s for each new grade, May said.

What Honda Thinks

Jeff Jetter from Honda said his company plans to use lower-viscosity oils, and sees the use of such oils as helping to develop new engine technologies. He said this also is potentially the last change in J300 due to the electrification of internal combustion engines. Honda wants to capture every bit of technical advantage through the use of low-viscosity engine oils.

Jetter proposed adding four new viscosity grades (Figure 1). While not offering specific limits, only approximate ones, the proposal did have a twist: Instead of HTHS overlap and no kinematic viscosity overlap, as is the current case, HTHS viscosity would not overlap and KV would. Honda believes that with this system, each OEM can choose the optimum oil for its engines.

Sliding wear is the most critical issue facing Honda and its engines, Jetter said. He provided data showing that the lightest oil (referred to as Category 5 and described in SAE paper 2011-01-1247) gave satisfactory antiwear performance in current production engines providing good protection from connecting rod wear at high speeds and temperatures, even using nonadditized mineral base oils.

While Honda is satisfied with the protection offered, Category 5 oils will not be applied to existing engines, Jetter added, because some components rely on oil pressure to function. However, future engine designs can be optimized to operate with this oil, he added.

Toyota and Others Minoru Yamashita reported that Toyota wanted to see a change in SAE 20 grade to a higher minimum viscosity and that a new grade be introduced which had a lower KV range as well as a lower HTHS minimum. The new viscosity grade could result in fuel economy improvements of up to 0.7 percent due solely to viscosity, according to Toyota.

Ron Romano of Ford Motor noted that it would be important to manage the spread in kinematic viscosity limits, as it affects hydraulic specifications, and engine oils are also expected to perform some hydraulic functions in automotive engines. While the test measurements are carried out over a narrow temperature range, the actual calibration of hydraulics is over a much greater range of temperatures. Tracey King of Chrysler concurred with Romano in this assessment.

Also during the meeting, Isabella Goldmints of Infineum offered data on a series of blended oils using API Group III and Group IV (polyalphaolefin) base stocks. All of the blends had an ILSAC GF-5 additive system, and nine of the blends contained no viscosity index improver. She said the results show its possible to blend oils with HTHS viscosity down to about 1.5 mPa-s – but at the expense of higher volatility. Noack volatility losses in some cases were as high as 23.4 percent or 27.9 percent – far beyond the 15 percent maximum evaporative loss allowed for GF-5 engine oils.

Goldmints pointed out that these data were viscometric in nature only, with no other performance claims intended.

Mike Covitch and Gail Evans of Lubrizol offered data and a proposal to split viscosity grades – essentially a high and low range for each grade. They cautioned that it would be important to define HTHS limits while also defining kinematic viscosity ranges that are needed for consistent hydraulic performance and which can be practically manufactured.

David Baillargeon of ExxonMobil offered his companys view of what lower viscosity limits should look like (Figure 2). This proposal – which would add SAE 10 and SAE 15 to the slate – was based on a Honda/SK proposal heard in January. ExxonMobil sees these as the only needed viscosity extensions, he indicated.

Why 0.3?

Questions were raised during the June meeting about the reason for the 0.3 mPa-s difference between grades and whether or not this is technically valid. Imperial Oils Chris May pointed out that this has historic precedent, with the difference between SAE 30 and 20 HTHSV limits being 0.3 mPa-s. He also noted that OEMs reportedly had run field durability tests on oils as low as 2.3 mPa-s HTHSV without wear problems but that lower values gave greater wear. Fords Ron Romano agreed that a wider difference could be of concern.

Savants Ted Selby presented data showing the correlation between the Multicell Capillary and Tapered Bearing Simulator test techniques for measuring HTHS viscosity. Based on the results of the work which was done in conjunction with Cannon Instruments, there will be a full correlation study done by ASTM subcommittee D7. This is important as the capillary procedure is used in some parts of the world instead of the Tapered Bearing Simulator, and SAE J300 is a global specification.

When May asked for feedback from the meeting attendees, Matthew Ansari of Chevron suggested that priorities needed to be identified in order to proceed. Ron Romano suggested that all proposals should be reviewed with an attempt to combine them into a single comprehensive proposal. He did caution that some thought should be given to sheared viscosity as opposed to new oil viscosities, because engines see sheared oil rather quickly.

Ongoing Issues

The group requested more specifics on viscometrics of the Honda and Toyota oils for further analysis. In addition, there was a lot of concern expressed about the risk of overlapping viscosities in the proposals. This is a reflection of the current system and its lack of overlap in any grade. In fact, there is a provision in J300 which specifically prohibits grade overlap. This will need to be reviewed if overlap is allowed.

The task force is waiting to hear further OEM input on needs and recommendations, including a Japanese Automobile Manufacturers Association discussion which occurred in late April. JAMA has indicated that a consensus position could not be reached, May said. Japanese OEMs instead are expected to provide their own individual proposals directly to the SAE task force. Feedback from North American OEMs will also be needed before any proposals advance from the working group.

The task force also must work on nomenclature issues in parallel with the grade limit proposals. Many in the industry have expressed concerns about how these new, lower viscosity oils will be identified for consumers.

Getting the nomenclature part of the definition right is critical they say, and using SAE 5, 10, or 15 has the potential for consumer confusion and misapplication. It may require a significant departure from the designations which have been used for almost 100 years.

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